Geometry Optimisation with CASTEP

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❍ ■ Atomic masses ■ The location of the pseudopotential libraries ■ External pressure that is to be applied to the supercell The .param file ■ General Job Parameters ■ Basis Set Parameters ■ Variable Cell Calculations ■ Electronic Minimisation Parameters ● ● Example - Bulk Silicon Outputs ❍ The .castep file ❍ The .geom file ❍ The .check file ❍ Other output files ● Checking the absolute convergence of our Bulk Silicon Calculation ● A Variable Cell calculation for Bulk Silicon. ● Example - A Bulk Terminated Silicon Surface ● References ● About this document ... 2005-04-04
Next: Inputs Up: Geometry Optimisation with CASTEP Previous: Geometry Optimisation with CASTEP Recipe The essence of the calculation is for the ions and electrons in the supercell to be moved around stepwise until the forces on the atoms and the change in total energy between steps fall below some predefined convergence tolerance. The ionic positions are optimised using quasi-Newton methods. For each configuration of the ionic positions the electronic configuration is optimised using the method of conjugated gradients. The flow of the calculation is thus; 1. Move ions into new positions using geometry optimisation algorithm 2. Optimise electronic configuration using conjugated gradients method 3. Compare total energy with previous configurations and check if forces within tolerance limits 4. If structure not optimised start at (1) and generate new set of ionic positions This cycle is performed until the forces fall within the tolerance limit and the energy should then be a local minimum. What types of system can this be applied to? In theory CASTEP can geometry optimise most bulk systems in a wide range of materials such as semiconductors, ceramics, metals, minerals and zeolites. It can also look at defects such as surfaces. The main restriction is the amount of computational resources available to the user. Calculations scale with the cube of the number of atoms included. More about this in the discussion of supercells. Next: Inputs Up: Geometry Optimisation with CASTEP Previous: Geometry Optimisation with CASTEP 2005-04-04
Page 1: Next: Recipe Geometry Optimisation
Page 5 and 6: Next: The Size and Shape Up: Inputs
Page 7 and 8: In both cases if [units] are not sp
Page 9 and 10: After the atomic symbol or the atom
Page 11 and 12: KPOINTS_MP_SPACING [units] Where is
Page 13 and 14: 2005-04-04
Page 15 and 16: Next: Atomic masses Up: The .cell f
Page 17 and 18: It is possible to fix the positions
Page 19 and 20: Next: External pressure that is Up:
Page 21 and 22: Next: General Job Parameters Up: In
Page 23 and 24: When a calculation that was stopped
Page 25 and 26: Next: Electronic Minimisation Param
Page 27 and 28: Next: Example - Bulk Silicon Up: Th
Page 29 and 30: the default value is 3 but it must
Page 31 and 32: We must now choose a supercell to e
Page 33 and 34: Next: The .castep file Up: Geometry
Page 35 and 36: 4 -2.14844155E+002 -9.84322032E-003
Page 37 and 38: BFGS: Final Configuration: ========
Page 39 and 40: Next: Other output files Up: Output
Page 41 and 42: Next: A Variable Cell calculation U
Page 43 and 44: arbitrary set of basis set paramete
Page 45 and 46: 3 -2.16474423E+002 2.10512829E-007
Page 47 and 48: Figure 6:A finite vacuum gap may ca
Page 49 and 50: 0.0000000000 0.0000000000 24.503725
Page 51 and 52: thickness We can see that the total
Page 53 and 54:
It is interesting to look at the ev
Page 55 and 56:
Next: About this document ... Up: G
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Geometry Optimisation with CASTEP

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