| Project/Area Number |
09640470
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
物性一般(含基礎論)
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| Research Institution | Keio University |
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Principal Investigator |
NOSE Shuichi Department of Physics, Faculty of Science and Technology, Keio University, Associate Professor, 理工学部, 助教授 (30172795)
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| Co-Investigator(Kenkyū-buntansha) |
能勢 修一 慶應義塾大学, 理工学部, 助教授 (30172795)
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| Project Period (FY) |
1997 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 1999: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1997: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | Car-Parrinello method / molecular dynamics simulations / structural phase transitions / fisrt-principles molecular dynamics simulations / Car-Parrinello法 |
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| Research Abstract |
A first-principles molecular dynamics simulation method which enables the study of structural phase transitions in covalent or metallic systems is developed combining electronic state calculations by Car-Parrinello method and a constant pressure method proposed by Parrinello and Rahman. The method is tested in 8 Si atom and 64 Si atom systems and phase transitions are observed directly in simulations during compression or decompression processes.
During the developing process of the method, we studied on following two themes.
1. The total momentum of ions is no longer conserved in the Car-Parrinello method. But a conservation law is still held if quantities relating to wave functions are included. An effect caused by introduction of thermostats is also investigated.
2. To express metallic states realistically, the partial occupation of energy levels should be allowed. Several methods are tested and we concluded that a method in which the weighting factor is expressed by Fermi distribution of the energy is most stable and suited for dynamical simulations.
Costs for computation of electronic state calculations increase considerably by combination with a constant pressure method. Simulations with high accuracy is very hard at present and several disagreement with experimental results are observed in our simulations. The shape of a unit cell in metallic phases deforms slightly and the crystal symmetry is changed. Structures obtained via structural phase transitions do not always agree with known structures. We confirmed that the deformation of the unit cell decreases by increasing the number of k point sampling in Brillouin zone and taking into consideration partial occupation of energy levels.
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