Geometry Optimisation with CASTEP

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Next: Checking the absolute convergence Up: Outputs Previous: The .check file Other output files .wvfn.nnnn this file contains a record of the wavefunction. The presence of this file allows a secondary restart mechanism. In the param file set ELEC_RESTORE_FILE To the root name. .bands this file contains the electronic eigenvalues related to the individual k-points. .err.nnnn this is an error file, written by every MPI process. If a job terminates unexpectedly this file will provide a ready source of diagnostic information. nnnn is the MPI rank. A job run in parallel on, say, 4 processors will return up to 4 .err. files depending on which nodes the problem has occured. If the calculation is run in serial without MPI then nnnn = 0001. 2005-04-04
Next: A Variable Cell calculation Up: Geometry Optimisation with CASTEP Previous: Other output files Checking the absolute convergence of our Bulk Silicon Calculation The example calculation with bulk silicon does not produce a very accurate answer. Can it be improved? There are two main sources of error in our calculation; ● ● Fundamental errors associated with the approximations used in the calculation such as the use of the LDA. Systematic errors associated with inaccuracies in the wavefunctions introduced by using a finite basis set and wavefunction sampling in reciprocal space. The latter of these must be reduced to a minimum. To show how this might be done I have repeated the calculation several times with increasing precision in the basis set and with various MP grid densities. Figure 3 below shows the total energy as a function of the basis set size for calculations with 1, 10, 28 and 60 K-Points. (See the section on variable cell calculations for a neat trick to efficiently perform many singlepoint energy calculations at a variety of cutoff energies at a fixed k-point density).
Page 1 and 2: Next: Recipe Geometry Optimisation
Page 3 and 4: Next: Inputs Up: Geometry Optimisat
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
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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: Next: Other output files Up: Output
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

Geometry Optimisation with CASTEP

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