13 results
Possible superconductivity in Bismuth (111) bilayers. Their electronic and vibrational properties from first principles
- David Hinojosa-Romero, Isaías Rodriguez, Alexander Valladares, Renela M. Valladares, Ariel A. Valladares
-
- Journal:
- MRS Advances / Volume 3 / Issue 6-7 / 2018
- Published online by Cambridge University Press:
- 29 January 2018, pp. 313-319
- Print publication:
- 2018
-
- Article
- Export citation
-
Using a 72-atom supercell we report ab initio calculations of the electronic and vibrational densities of states for the bismuth (111) bilayers (bismuthene) with periodic boundary conditions and a vacuum of 5 Å, 10 Å and 20 Å. We find that the electronic density of states shows a metallic character at the Fermi level and that the vibrational density of states manifests the expected gap due to the layers. Our results indicate that a vacuum down to 5 Å does not affect the electronic and vibrational structures noticeably. A comparison of present results with those obtained for the Wyckoff structure is displayed. Assuming that the Cooper pairing potential is similar for all phases and structures of bismuth, an estimate of the superconducting transition temperature gives 2.61 K for the bismuth bilayers.
Compressed Crystalline Bismuth and Superconductivity ̶ An ab initio computational Simulation
- David Hinojosa-Romero, Isaías Rodríguez, Zaahel Mata-Pinzón, Alexander Valladares, Renela Valladares, Ariel A. Valladares
-
- Journal:
- MRS Advances / Volume 2 / Issue 9 / 2017
- Published online by Cambridge University Press:
- 20 January 2017, pp. 499-506
- Print publication:
- 2017
-
- Article
- Export citation
-
Bismuth displays puzzling superconducting properties. In its crystalline equilibrium phase, it does not seem to superconduct at accessible low temperatures. However, in the amorphous phase it displays superconductivity at ∼ 6 K. Under pressure bismuth has been found to superconduct at Tcs that go from 3.9 K to 8.5 K depending on the phase obtained. So the question is: what electronic or vibrational changes occur that explains this radical transformation in the conducting behavior of this material? In a recent publication we argue that changes in the density of electronic and vibrational states may account for the behavior observed in the amorphous phase with respect to the crystal. We have now undertaken an ab initio computational study of the effects of pressure alone maintaining the original crystalline structure and compressing our supercell computationally. From the results obtained we infer that if the crystal structure remains the same (except for the contraction), no superconductivity will appear.
Amorphous Bismuth: Structure-Property Relations and the Size of the Supercell
- Zaahel Mata-Pinzón, Ariel A. Valladares, Alexander Valladares, R. M. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1520 / 2013
- Published online by Cambridge University Press:
- 23 January 2013, mrsf12-1520-nn09-11
- Print publication:
- 2013
-
- Article
- Export citation
-
It has been argued that for the simulation of amorphous materials, the larger the periodic supercell the better the representation. We contend that for certain properties there is a minimum supercell size above which one obtains a good representation of the topological and electronic collective properties of the material independent of the size. To show this contention we have chosen two periodic supercells of bismuth, one with 64 atoms and another with 216 atoms, which were amorphized using our undermelt-quench approach [1]. The originally crystalline structures were subjected to a heating-and-cooling process starting at an initial temperature of 300 K and linearly going up to 540 K, in 100 simulational steps, 4.5 K just below the melting temperature of bismuth (the undermelt section of the process) under normal conditions of pressure. Next, the sample was cooled down to 0K (the quench section of the process), in 225 simulational steps with the same absolute cooling rate as the heating process. Then the samples obtained were geometry-optimized to find the final metastable amorphous structures. These structures were analyzed by calculating their radial (pair) distribution functions, the plane angle distributions and the electron densities of states. Results will be presented that manifest that after proper normalization due to the difference in the number of atoms and the number of electron energy levels, the two structures are, for all practical purpose, the same, indicating that in this case, the size of the cell does not seem to play a major role in the properties determined.
Structural and Electronic Properties of Cu64Zr36 BMG by ab initio Molecular Dynamics
- Jonathan Galván-Colín, Ariel A. Valladares, Alexander Valladares, Renela M. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1517 / 2013
- Published online by Cambridge University Press:
- 25 January 2013, mrsf12-1517-kk05-03
- Print publication:
- 2013
-
- Article
- Export citation
-
Much attention has been given to bulk metallic glasses (BMG) in recent years, particularly those based on binary alloys due to the simplicity of their atomic composition. Although efforts to understand the atomistic features that give rise to their exceptional properties have been made, the electronic and vibrational properties have been disregarded. We undertook the task of simulating the Cu64Zr36 glassy metal using a supercell with 108 atoms and a different simulational approach: the undermelt-quench approach [1]. The structure was characterized by means of the radial (pair) distribution function and the bond-angle distribution and the electronic density of states was calculated. We find that our results agree well with experimental data.
Contributors
-
- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. Hackett, Getatchew Haile, Douglas John Hall, Nicholas Hammond, Daphne Hampson, Jehu J. Hanciles, Barry Hankins, Jennifer Haraguchi, Stanley S. Harakas, Anthony John Harding, Conrad L. Harkins, J. William Harmless, Marjory Harper, Amir Harrak, Joel F. Harrington, Mark W. Harris, Susan Ashbrook Harvey, Van A. Harvey, R. Chris Hassel, Jione Havea, Daniel Hawk, Diana L. Hayes, Leslie Hayes, Priscilla Hayner, S. Mark Heim, Simo Heininen, Richard P. Heitzenrater, Eila Helander, David Hempton, Scott H. Hendrix, Jan-Olav Henriksen, Gina Hens-Piazza, Carter Heyward, Nicholas J. Higham, David Hilliard, Norman A. Hjelm, Peter C. Hodgson, Arthur Holder, M. Jan Holton, Dwight N. Hopkins, Ronnie Po-chia Hsia, Po-Ho Huang, James Hudnut-Beumler, Jennifer S. Hughes, Leonard M. Hummel, Mary E. Hunt, Laennec Hurbon, Mark Hutchinson, Susan E. Hylen, Mary Beth Ingham, H. Larry Ingle, Dale T. Irvin, Jon Isaak, Paul John Isaak, Ada María Isasi-Díaz, Hans Raun Iversen, Margaret C. Jacob, Arthur James, Maria Jansdotter-Samuelsson, David Jasper, Werner G. Jeanrond, Renée Jeffery, David Lyle Jeffrey, Theodore W. Jennings, David H. Jensen, Robin Margaret Jensen, David Jobling, Dale A. Johnson, Elizabeth A. Johnson, Maxwell E. Johnson, Sarah Johnson, Mark D. Johnston, F. Stanley Jones, James William Jones, John R. Jones, Alissa Jones Nelson, Inge Jonsson, Jan Joosten, Elizabeth Judd, Mulambya Peggy Kabonde, Robert Kaggwa, Sylvester Kahakwa, Isaac Kalimi, Ogbu U. Kalu, Eunice Kamaara, Wayne C. Kannaday, Musimbi Kanyoro, Veli-Matti Kärkkäinen, Frank Kaufmann, Léon Nguapitshi Kayongo, Richard Kearney, Alice A. Keefe, Ralph Keen, Catherine Keller, Anthony J. Kelly, Karen Kennelly, Kathi Lynn Kern, Fergus Kerr, Edward Kessler, George Kilcourse, Heup Young Kim, Kim Sung-Hae, Kim Yong-Bock, Kim Yung Suk, Richard King, Thomas M. King, Robert M. Kingdon, Ross Kinsler, Hans G. Kippenberg, Cheryl A. Kirk-Duggan, Clifton Kirkpatrick, Leonid Kishkovsky, Nadieszda Kizenko, Jeffrey Klaiber, Hans-Josef Klauck, Sidney Knight, Samuel Kobia, Robert Kolb, Karla Ann Koll, Heikki Kotila, Donald Kraybill, Philip D. W. Krey, Yves Krumenacker, Jeffrey Kah-Jin Kuan, Simanga R. Kumalo, Peter Kuzmic, Simon Shui-Man Kwan, Kwok Pui-lan, André LaCocque, Stephen E. Lahey, John Tsz Pang Lai, Emiel Lamberts, Armando Lampe, Craig Lampe, Beverly J. Lanzetta, Eve LaPlante, Lizette Larson-Miller, Ariel Bybee Laughton, Leonard Lawlor, Bentley Layton, Robin A. Leaver, Karen Lebacqz, Archie Chi Chung Lee, Marilyn J. Legge, Hervé LeGrand, D. L. LeMahieu, Raymond Lemieux, Bill J. Leonard, Ellen M. Leonard, Outi Leppä, Jean Lesaulnier, Nantawan Boonprasat Lewis, Henrietta Leyser, Alexei Lidov, Bernard Lightman, Paul Chang-Ha Lim, Carter Lindberg, Mark R. Lindsay, James R. Linville, James C. Livingston, Ann Loades, David Loades, Jean-Claude Loba-Mkole, Lo Lung Kwong, Wati Longchar, Eleazar López, David W. Lotz, Andrew Louth, Robin W. Lovin, William Luis, Frank D. Macchia, Diarmaid N. J. MacCulloch, Kirk R. MacGregor, Marjory A. MacLean, Donald MacLeod, Tomas S. Maddela, Inge Mager, Laurenti Magesa, David G. Maillu, Fortunato Mallimaci, Philip Mamalakis, Kä Mana, Ukachukwu Chris Manus, Herbert Robinson Marbury, Reuel Norman Marigza, Jacqueline Mariña, Antti Marjanen, Luiz C. L. Marques, Madipoane Masenya (ngwan'a Mphahlele), Caleb J. D. Maskell, Steve Mason, Thomas Massaro, Fernando Matamoros Ponce, András Máté-Tóth, Odair Pedroso Mateus, Dinis Matsolo, Fumitaka Matsuoka, John D'Arcy May, Yelena Mazour-Matusevich, Theodore Mbazumutima, John S. McClure, Christian McConnell, Lee Martin McDonald, Gary B. McGee, Thomas McGowan, Alister E. McGrath, Richard J. McGregor, John A. McGuckin, Maud Burnett McInerney, Elsie Anne McKee, Mary B. McKinley, James F. McMillan, Ernan McMullin, Kathleen E. McVey, M. Douglas Meeks, Monica Jyotsna Melanchthon, Ilie Melniciuc-Puica, Everett Mendoza, Raymond A. Mentzer, William W. Menzies, Ina Merdjanova, Franziska Metzger, Constant J. Mews, Marvin Meyer, Carol Meyers, Vasile Mihoc, Gunner Bjerg Mikkelsen, Maria Inêz de Castro Millen, Clyde Lee Miller, Bonnie J. Miller-McLemore, Alexander Mirkovic, Paul Misner, Nozomu Miyahira, R. W. L. Moberly, Gerald Moede, Aloo Osotsi Mojola, Sunanda Mongia, Rebeca Montemayor, James Moore, Roger E. Moore, Craig E. Morrison O.Carm, Jeffry H. Morrison, Keith Morrison, Wilson J. Moses, Tefetso Henry Mothibe, Mokgethi Motlhabi, Fulata Moyo, Henry Mugabe, Jesse Ndwiga Kanyua Mugambi, Peggy Mulambya-Kabonde, Robert Bruce Mullin, Pamela Mullins Reaves, Saskia Murk Jansen, Heleen L. Murre-Van den Berg, Augustine Musopole, Isaac M. T. Mwase, Philomena Mwaura, Cecilia Nahnfeldt, Anne Nasimiyu Wasike, Carmiña Navia Velasco, Thulani Ndlazi, Alexander Negrov, James B. Nelson, David G. Newcombe, Carol Newsom, Helen J. Nicholson, George W. E. Nickelsburg, Tatyana Nikolskaya, Damayanthi M. A. Niles, Bertil Nilsson, Nyambura Njoroge, Fidelis Nkomazana, Mary Beth Norton, Christian Nottmeier, Sonene Nyawo, Anthère Nzabatsinda, Edward T. Oakes, Gerald O'Collins, Daniel O'Connell, David W. Odell-Scott, Mercy Amba Oduyoye, Kathleen O'Grady, Oyeronke Olajubu, Thomas O'Loughlin, Dennis T. Olson, J. Steven O'Malley, Cephas N. Omenyo, Muriel Orevillo-Montenegro, César Augusto Ornellas Ramos, Agbonkhianmeghe E. Orobator, Kenan B. Osborne, Carolyn Osiek, Javier Otaola Montagne, Douglas F. Ottati, Anna May Say Pa, Irina Paert, Jerry G. Pankhurst, Aristotle Papanikolaou, Samuele F. Pardini, Stefano Parenti, Peter Paris, Sung Bae Park, Cristián G. Parker, Raquel Pastor, Joseph Pathrapankal, Daniel Patte, W. Brown Patterson, Clive Pearson, Keith F. Pecklers, Nancy Cardoso Pereira, David Horace Perkins, Pheme Perkins, Edward N. Peters, Rebecca Todd Peters, Bishop Yeznik Petrossian, Raymond Pfister, Peter C. Phan, Isabel Apawo Phiri, William S. F. Pickering, Derrick G. Pitard, William Elvis Plata, Zlatko Plese, John Plummer, James Newton Poling, Ronald Popivchak, Andrew Porter, Ute Possekel, James M. Powell, Enos Das Pradhan, Devadasan Premnath, Jaime Adrían Prieto Valladares, Anne Primavesi, Randall Prior, María Alicia Puente Lutteroth, Eduardo Guzmão Quadros, Albert Rabil, Laurent William Ramambason, Apolonio M. Ranche, Vololona Randriamanantena Andriamitandrina, Lawrence R. Rast, Paul L. Redditt, Adele Reinhartz, Rolf Rendtorff, Pål Repstad, James N. Rhodes, John K. Riches, Joerg Rieger, Sharon H. Ringe, Sandra Rios, Tyler Roberts, David M. Robinson, James M. Robinson, Joanne Maguire Robinson, Richard A. H. Robinson, Roy R. Robson, Jack B. Rogers, Maria Roginska, Sidney Rooy, Rev. Garnett Roper, Maria José Fontelas Rosado-Nunes, Andrew C. Ross, Stefan Rossbach, François Rossier, John D. Roth, John K. Roth, Phillip Rothwell, Richard E. Rubenstein, Rosemary Radford Ruether, Markku Ruotsila, John E. Rybolt, Risto Saarinen, John Saillant, Juan Sanchez, Wagner Lopes Sanchez, Hugo N. Santos, Gerhard Sauter, Gloria L. Schaab, Sandra M. Schneiders, Quentin J. Schultze, Fernando F. Segovia, Turid Karlsen Seim, Carsten Selch Jensen, Alan P. F. Sell, Frank C. Senn, Kent Davis Sensenig, Damían Setton, Bal Krishna Sharma, Carolyn J. Sharp, Thomas Sheehan, N. Gerald Shenk, Christian Sheppard, Charles Sherlock, Tabona Shoko, Walter B. Shurden, Marguerite Shuster, B. Mark Sietsema, Batara Sihombing, Neil Silberman, Clodomiro Siller, Samuel Silva-Gotay, Heikki Silvet, John K. Simmons, Hagith Sivan, James C. Skedros, Abraham Smith, Ashley A. Smith, Ted A. Smith, Daud Soesilo, Pia Søltoft, Choan-Seng (C. S.) Song, Kathryn Spink, Bryan Spinks, Eric O. Springsted, Nicolas Standaert, Brian Stanley, Glen H. Stassen, Karel Steenbrink, Stephen J. Stein, Andrea Sterk, Gregory E. Sterling, Columba Stewart, Jacques Stewart, Robert B. Stewart, Cynthia Stokes Brown, Ken Stone, Anne Stott, Elizabeth Stuart, Monya Stubbs, Marjorie Hewitt Suchocki, David Kwang-sun Suh, Scott W. Sunquist, Keith Suter, Douglas Sweeney, Charles H. Talbert, Shawqi N. Talia, Elsa Tamez, Joseph B. Tamney, Jonathan Y. Tan, Yak-Hwee Tan, Kathryn Tanner, Feiya Tao, Elizabeth S. Tapia, Aquiline Tarimo, Claire Taylor, Mark Lewis Taylor, Bishop Abba Samuel Wolde Tekestebirhan, Eugene TeSelle, M. Thomas Thangaraj, David R. Thomas, Andrew Thornley, Scott Thumma, Marcelo Timotheo da Costa, George E. “Tink” Tinker, Ola Tjørhom, Karen Jo Torjesen, Iain R. Torrance, Fernando Torres-Londoño, Archbishop Demetrios [Trakatellis], Marit Trelstad, Christine Trevett, Phyllis Trible, Johannes Tromp, Paul Turner, Robert G. Tuttle, Archbishop Desmond Tutu, Peter Tyler, Anders Tyrberg, Justin Ukpong, Javier Ulloa, Camillus Umoh, Kristi Upson-Saia, Martina Urban, Monica Uribe, Elochukwu Eugene Uzukwu, Richard Vaggione, Gabriel Vahanian, Paul Valliere, T. J. Van Bavel, Steven Vanderputten, Peter Van der Veer, Huub Van de Sandt, Louis Van Tongeren, Luke A. Veronis, Noel Villalba, Ramón Vinke, Tim Vivian, David Voas, Elena Volkova, Katharina von Kellenbach, Elina Vuola, Timothy Wadkins, Elaine M. Wainwright, Randi Jones Walker, Dewey D. Wallace, Jerry Walls, Michael J. Walsh, Philip Walters, Janet Walton, Jonathan L. Walton, Wang Xiaochao, Patricia A. Ward, David Harrington Watt, Herold D. Weiss, Laurence L. Welborn, Sharon D. Welch, Timothy Wengert, Traci C. West, Merold Westphal, David Wetherell, Barbara Wheeler, Carolinne White, Jean-Paul Wiest, Frans Wijsen, Terry L. Wilder, Felix Wilfred, Rebecca Wilkin, Daniel H. Williams, D. Newell Williams, Michael A. Williams, Vincent L. Wimbush, Gabriele Winkler, Anders Winroth, Lauri Emílio Wirth, James A. Wiseman, Ebba Witt-Brattström, Teofil Wojciechowski, John Wolffe, Kenman L. Wong, Wong Wai Ching, Linda Woodhead, Wendy M. Wright, Rose Wu, Keith E. Yandell, Gale A. Yee, Viktor Yelensky, Yeo Khiok-Khng, Gustav K. K. Yeung, Angela Yiu, Amos Yong, Yong Ting Jin, You Bin, Youhanna Nessim Youssef, Eliana Yunes, Robert Michael Zaller, Valarie H. Ziegler, Barbara Brown Zikmund, Joyce Ann Zimmerman, Aurora Zlotnik, Zhuo Xinping
- Edited by Daniel Patte, Vanderbilt University, Tennessee
-
- Book:
- The Cambridge Dictionary of Christianity
- Published online:
- 05 August 2012
- Print publication:
- 20 September 2010, pp xi-xliv
-
- Chapter
- Export citation
Are Slit Pores in Carbonaceus Materials Real?
- Cristina Romero, Ariel A. Valladares, R. M. Valladares, Alexander Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1216 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1216-W08-13
- Print publication:
- 2009
-
- Article
- Export citation
-
Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. The slit pore model is one of the oldest models proposed to describe porous carbon. Developed by Emmet in 1948 [1] it has been recurrently used and in its most basic form consists of two parallel graphene layers separated by a distance that is taken as the width of the pore. Its simplicity limits its applicability since experimental evidence suggests that the walls of the carbon pores have widths of a few graphene layers [2], but it still is appealing for computational simulations due to its low computational cost. Using a previously developed ab initio approach to generate porous semiconductors [3] we have obtained porous carbonaceous materials with walls made up of a few graphene layers (four layers), in agreement with experimental results; these walls are separated by distances comparable to those used in the slit pore model [4]. This validates the idea of a modified slit pore model obtained without the use of ad hoc suppositions. Structures will be presented, analyzed and compared to available experimental results.
Could Porosity Induce Gaps in the Vibrational Density of States of Nanoporous Silicon?
- Juan Carlos Noyola, Alexander Valladares, R. M. Valladares, Ariel A. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1221 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1221-CC07-11
- Print publication:
- 2009
-
- Article
- Export citation
-
As in our previous work [1] nanoporous silicon periodic supercells with 1000 atoms but now with 80 % porosity were constructed using the Tersoff potential and our novel approach [2]. The approach consists first in constructing a crystalline diamond-like supercell with a density (volume) close to the real value, and then lowering the density by increasing the volume, subjecting the resulting periodic supercell to Tersoff-based molecular dynamics processes at a temperature of 300 K, followed by geometry relaxation [1]. As in the ab initio approach [2] the resulting samples are also essentially amorphous and display pores along some of the crystallographic directions. We report the radial (pair) distribution function (RDF), g(r), the bond angle distribution, the pore structure where prominent and a computational prediction for the vibrational density of states for this structure. We then compare it to the 50 % porous sample presented in Ref [1]. The soft acoustic phonons are displaced towards lower energy in the 80 % porosity sample whereas the optical modes are displaced towards higher energies. The pseudo gap, existing in the 50 % porous sample, is depleted even more in the 80 % sample indicating a tendency towards the creation of a phonon gap for higher porosity materials. Some conjectures that point to the possible engineering of porous materials to produce predetermined phonon properties are discussed.
Ab initio Computationally Generated Nanoporous Carbon and its Comparison to Experiment
- Cristina Romero, Ariel A. Valladares, R. M. Valladares, Alexander Valladares, Alipio G. Calles
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1145 / 2008
- Published online by Cambridge University Press:
- 01 February 2011, 1145-MM04-27
- Print publication:
- 2008
-
- Article
- Export citation
-
Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. Here we present an application of our recently developed ab initio method [1] for the generation of group IV porous materials. The method consists in constructing a crystalline diamond supercell with 216 atoms of carbon and a density of 3.546 g/cm3, then lengthening the supercell edge to obtain a density of 1.38 g/cm3, yielding a porosity of 61.1 % in order to be able to compare with experimental results reported in the literature [2]. We then subject the resulting supercell to an ab initio molecular dynamics process at 1000 K during 295 steps. The radial distribution functions obtained are compared to experiment to discern coincidences and discrepancies.
Hydrogen adsorbed in ab initio computationally simulated nanoporous carbon. An energetics study
- R. M. Valladares, Alexander Valladares, A. G. Calles, Ariel A. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 1042 / 2007
- Published online by Cambridge University Press:
- 01 February 2011, 1042-S03-28
- Print publication:
- 2007
-
- Article
- Export citation
-
Nanoporous carbon has been considered an interesting and potentially useful material for storing hydrogen. Using nanoporous carbon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the carbon atoms were first saturated with hydrogen, then relaxed and its total energy calculated with and without hydrogen. Next the same number of hydrogen atoms, in molecular form, was randomly placed within the pore of the pure carbon supercell, then the sample relaxed, and finally its total energy calculated, also with and without hydrogens. From these results the average energy per hydrogen atom is obtained for both cases. For the molecular hydrogen sample the binding energy found per hydrogen atom is 343.89 meV, which compares favourably with values reported in the literature, 300-400 meV/molecule.
Computer Modeling of Nanoporous Materials: An ab initio Novel Approach for Silicon and Carbon
- Ariel A. Valladares, Alexander Valladares, R. M. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 988 / 2006
- Published online by Cambridge University Press:
- 26 February 2011, 0988-QQ09-15
- Print publication:
- 2006
-
- Article
- Export citation
-
Carbon and silicon have been consistently proposed as elements useful in the generation of porous materials. Carbon has been insistently postulated as a promising material to store hydrogen, and crystalline silicogermanate zeolites have recently been synthesized and are being considered in catalytic processes. In the present work we report an approach to generating porous materials, in particular porous carbon and silicon, which leads to the existence of nanopores within the bulk. The method consists in constructing a crystalline diamond-like supercell with 216 atoms with a density (volume) close to the real value, then halving the density by doubling the volume (50% porosity), and subjecting the resulting supercell to an ab initio molecular dynamics process at 300 K for Si, and 1000 K for carbon, followed by geometry relaxation. The resulting samples are essentially amorphous and display pores along some of the “crystallographic” directions. We report their radial distribution functions and the pore structure where prominent.
The Energetics of Hydrogen Adsorbed in Nanoporous Silicon. An ab initio Simulational Study
- Ariel A. Valladares, Alexander Valladares, R. M. Valladares, A. G. Calles
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 971 / 2006
- Published online by Cambridge University Press:
- 26 February 2011, 0971-Z07-08
- Print publication:
- 2006
-
- Article
- Export citation
-
Porous silicon may be an interesting alternative to store hydrogen. Unlike carbon, its bonding multiplicity is limited, and because of this, the probability of having more dangling bonds on the pore surface is larger than in carbon. Using nanoporous silicon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the silicon atoms were first saturated with hydrogen, then relaxed and its total energy calculated. Next the same number of hydrogen atoms was placed within the pore in the pure silicon supercell, then the sample relaxed, and finally its total energy calculated, with and without hydrogens. From these results the average energy per hydrogen atom is obtained. We compare our results to SiH bond energies and to previous results for hydrogenated carbon; conclusions are drawn concerning the possibility of using porous silicon as a fuel tank for hydrogen.
Structural properties of amorphous aluminum and aluminum-nitrogen alloys. Computer simulations
- Ariel A. Valladares, Alexander Valladares, R. M. Valladares, A. Calles
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 848 / 2004
- Published online by Cambridge University Press:
- 01 February 2011, FF9.29
- Print publication:
- 2004
-
- Article
- Export citation
-
Liquid and amorphous metallic systems have proven difficult to model. Some efforts have relied on the use of parameterized classical potentials of the Lennard-Jones type or geometric hard sphere simulations, but first principles approaches have been rarely used. Clearly a knowledge of atomic structures is paramount for calculating physical properties. In this work we apply our recently developed ab initio DFT approach (A. A. Valladares et al., Eur. Phys. J. 22 (2001) 443) for the generation of amorphous semiconducting materials, to amorphize aluminum and an aluminum-nitrogen alloy. We report radial distribution functions (RDFs) and specific atomic structures of periodic amorphous/liquid cubic supercells of 108 atoms with a volume of (12.1485 Å)3, generated using the Harris functional.
The Influence of 5- and 6-Atom Rings on the Optical Properties of Amorphous Silicon Nitride. A Cluster Simulation
- R.M. Valladarest, A.G. Calles, Alexander Valladares, Ariel A. Valladares
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 579 / 1999
- Published online by Cambridge University Press:
- 15 February 2011, 103
- Print publication:
- 1999
-
- Article
- Export citation
-
We simulate α - Si21 –N2: H that contains 6-atom boat-type rings and a – Si17–iNi: H that contains 5-atom planar rings, where i = 0, 1 or 4. The simulations were carried out using the DFT-LDA approximation contained in the DMol code of MSI. We report calculations of impurity levels and relate these to the size of the gap and to the optical absorption curves for each cluster. A comparison is made between the two α – SiN clusters studied to analyze the effect of the ring topology.