[Wien] Suggestions on the Hellmann-Feynman Force File : analyse_phonon_lapw

[Peter Blaha]

In principle the sum of forces should be exactly zero, in practice they never are.
This can be: lack of scf convergence, or too small RKmax, or K-points, or numerics (spheres,....)

Your forces look "reasonable", but:

"Test" your results:

a) Calculate phonons with these forces.
b) continue the scf (eg. -fc 0.05) and recalculate phonons. How much did they differ ?
c) increase (of if already large, decrease) RKMAX and check how much phonons change.
d) increase/decrease k-mesh ---> how do phonons change.

Am 20.01.2011 07:36, schrieb Ghosh SUDDHASATTWA:
> Dear Wien2k users,
>
> I have carried out the phonon calculations on AB2 system and after analyse_phonon_lapw, I get the following
>
> Sum of forces (should be zero) for case 1: 0.1140 0.0000 0.0000
>
> Sum of forces (should be zero) for case 2: -0.1000 0.0000 -0.0160
>
> Sum of forces (should be zero) for case 3: 0.0010 0.0390 -0.0030
>
> Sum of forces (should be zero) for case 4: 0.0010 -0.0270 -0.0080
>
> Sum of forces (should be zero) for case 5: 0.0060 0.0000 0.0810
>
> Sum of forces (should be zero) for case 6: 0.0120 0.0000 -0.1070
>
> Sum of forces (should be zero) for case 7: -0.0120 0.0000 0.0070
>
> Sum of forces (should be zero) for case 8: 0.0140 0.0000 -0.0060
>
> Sum of forces (should be zero) for case 9: 0.0040 -0.0160 0.0050
>
> Sum of forces (should be zero) for case 10: 0.0090 -0.0060 -0.0100
>
> Sum of forces (should be zero) for case 11: 0.0100 0.0000 0.0260
>
> Sum of forces (should be zero) for case 12: 0.0060 0.0000 -0.0230
>
> Sum of forces (should be zero) for case 13: -0.1000 0.0000 0.0010
>
> Sum of forces (should be zero) for case 14: 0.1050 0.0000 0.0110
>
> Sum of forces (should be zero) for case 15: 0.0060 -0.0180 0.0100
>
> Sum of forces (should be zero) for case 16: -0.0010 0.0310 -0.0070
>
> Sum of forces (should be zero) for case 17: 0.0020 0.0000 -0.1310
>
> Sum of forces (should be zero) for case 18: -0.0060 0.0000 0.1320
>
> Sum of forces of all displacements: 0.5090 0.1370 0.5840
>
> displacements 1 and 2 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 3 0.093 0.000 2.645
>
> 3 -0.094 0.000 2.193
>
> displacements 3 and 4 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> displacements 5 and 6 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 2 -0.012 0.000 -9.745
>
> 2 -0.014 0.000 5.051
>
> atom 3 0.231 0.000 3.018
>
> 3 -0.195 0.000 1.870
>
> atom 4 -0.206 0.000 3.023
>
> 4 0.224 0.000 1.867
>
> displacements 7 and 8 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 3 1.531 0.000 3.489
>
> 3 -1.356 0.000 1.401
>
> displacements 9 and 10 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> displacements 11 and 12 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 3 1.005 0.000 3.046
>
> 3 -0.942 0.000 1.807
>
> atom 4 -0.974 0.000 3.041
>
> 4 0.964 0.000 1.799
>
> displacements 13 and 14 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 1 1.719 0.000 -3.421
>
> 1 -1.894 0.000 -1.350
>
> atom 12 0.719 0.000 31.755
>
> 12 -0.516 0.000 31.834
>
> displacements 15 and 16 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> displacements 17 and 18 can be symmetrized
>
> The following forces differ by more than 20 %:
>
> atom 4 0.018 0.000 4.296
>
> 4 0.013 0.000 0.301
>
> atom 10 0.000 0.000 -37.751
>
> 10 0.000 0.000 -25.822
>
> Sum of forces of all symm.displ: 0.0000 0.0000 0.0000
>
> I need the suggestion on if the forces are ok ????
>
> ( The command in run_phonon was run_lapw –I –i 200 –cc 0.0001 –in1ef –p –fc 0.1)
>
> Or it requires still more accurate forces (with fc 0.01 or lesser)
>
> Thanks
>
> Suddhasattwa
>
>
>
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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