Phonon calculation

[novodo]

Hi everyone! I tried to calculate phonon frequencies for several simple structures (Li, LiH, MgH2...) obtaining always the following problem: output frequencies are wrong and they are spread over a large number of frequencies (without sense). I'm using finite displacement method as implemented in vasp 4.6 (so frequencies are at Gamma point).
Here i post frequencies I found in the OUTCAR file for simple Lithium, using a supercell 2x2x2 with 16 atoms inside:


1 f = 10.775875 THz 67.706817 2PiTHz 359.444478 cm-1 44.565451 meV
2 f = 10.562388 THz 66.365442 2PiTHz 352.323331 cm-1 43.682541 meV
3 f = 10.433510 THz 65.555674 2PiTHz 348.024408 cm-1 43.149543 meV
4 f = 10.394955 THz 65.313426 2PiTHz 346.738351 cm-1 42.990092 meV
5 f = 10.288666 THz 64.645597 2PiTHz 343.192955 cm-1 42.550519 meV
6 f = 10.286841 THz 64.634130 2PiTHz 343.132081 cm-1 42.542971 meV
7 f = 10.255906 THz 64.439761 2PiTHz 342.100205 cm-1 42.415035 meV
8 f = 10.147918 THz 63.761250 2PiTHz 338.498103 cm-1 41.968431 meV
9 f = 10.089047 THz 63.391350 2PiTHz 336.534361 cm-1 41.724958 meV
10 f = 8.530795 THz 53.600565 2PiTHz 284.556677 cm-1 35.280544 meV
11 f = 8.507036 THz 53.451281 2PiTHz 283.764157 cm-1 35.182284 meV
12 f = 8.165957 THz 51.308222 2PiTHz 272.387005 cm-1 33.771697 meV
13 f = 8.165579 THz 51.305846 2PiTHz 272.374389 cm-1 33.770132 meV
14 f = 8.164723 THz 51.300467 2PiTHz 272.345831 cm-1 33.766592 meV
15 f = 8.164679 THz 51.300191 2PiTHz 272.344365 cm-1 33.766410 meV
16 f = 8.164220 THz 51.297306 2PiTHz 272.329052 cm-1 33.764511 meV
17 f = 8.163626 THz 51.293576 2PiTHz 272.309248 cm-1 33.762056 meV
18 f = 7.694024 THz 48.342976 2PiTHz 256.644995 cm-1 31.819935 meV
19 f = 7.619496 THz 47.874704 2PiTHz 254.159014 cm-1 31.511713 meV
20 f = 7.124791 THz 44.766384 2PiTHz 237.657448 cm-1 29.465779 meV
21 f = 7.122801 THz 44.753881 2PiTHz 237.591075 cm-1 29.457549 meV
22 f = 7.122602 THz 44.752631 2PiTHz 237.584436 cm-1 29.456726 meV
23 f = 7.121930 THz 44.748409 2PiTHz 237.562023 cm-1 29.453948 meV
24 f = 7.121209 THz 44.743874 2PiTHz 237.537946 cm-1 29.450962 meV
25 f = 7.118281 THz 44.725476 2PiTHz 237.440274 cm-1 29.438853 meV
26 f = 7.104258 THz 44.637369 2PiTHz 236.972531 cm-1 29.380860 meV
27 f = 7.098524 THz 44.601341 2PiTHz 236.781261 cm-1 29.357145 meV
28 f = 7.098187 THz 44.599225 2PiTHz 236.770027 cm-1 29.355752 meV
29 f = 7.096560 THz 44.589003 2PiTHz 236.715764 cm-1 29.349025 meV
30 f = 6.900910 THz 43.359698 2PiTHz 230.189580 cm-1 28.539881 meV
31 f = 6.896810 THz 43.333937 2PiTHz 230.052822 cm-1 28.522925 meV
32 f = 6.846522 THz 43.017965 2PiTHz 228.375376 cm-1 28.314948 meV
33 f = 6.845430 THz 43.011103 2PiTHz 228.338950 cm-1 28.310432 meV
34 f = 6.845359 THz 43.010658 2PiTHz 228.336588 cm-1 28.310139 meV
35 f = 6.844171 THz 43.003192 2PiTHz 228.296952 cm-1 28.305225 meV
36 f = 6.351464 THz 39.907423 2PiTHz 211.862017 cm-1 26.267552 meV
37 f = 6.349910 THz 39.897662 2PiTHz 211.810197 cm-1 26.261127 meV
38 f = 3.568932 THz 22.424262 2PiTHz 119.046761 cm-1 14.759923 meV
39 f = 3.566894 THz 22.411455 2PiTHz 118.978770 cm-1 14.751493 meV
40 f = 2.027468 THz 12.738955 2PiTHz 67.629037 cm-1 8.384935 meV
41 f = 2.026815 THz 12.734852 2PiTHz 67.607257 cm-1 8.382235 meV
42 f = 1.633517 THz 10.263690 2PiTHz 54.488263 cm-1 6.755686 meV
43 f = 1.629616 THz 10.239178 2PiTHz 54.358128 cm-1 6.739551 meV
44 f = 1.151234 THz 7.233416 2PiTHz 38.401028 cm-1 4.761122 meV
45 f = 1.127359 THz 7.083405 2PiTHz 37.604644 cm-1 4.662383 meV
46 f/i= 0.000934 THz 0.005868 2PiTHz 0.031153 cm-1 0.003862 meV
47 f/i= 0.006251 THz 0.039279 2PiTHz 0.208527 cm-1 0.025854 meV
48 f/i= 0.110839 THz 0.696425 2PiTHz 3.697205 cm-1 0.458395 meV

The followings are INPUT files:

**********************************************************
INCAR
********************************************************

SYSTEM = Li

Startparameter for this Run:
NWRITE = 2; LPETIM=F
ISTART = 0

Electronic Relaxation
ENCUT = 350
NELM = 20;
EDIFF = 1E-04
Ionic Relaxation
NSW = 20
NBLOCK = 1; KBLOCK = 5
IBRION = 5
ISYM = 1
POTIM = 0.015
ISMEAR = 2; SIGMA = .20

IALGO = 38
LDIAG = T
LREAL = F

NGX=90; NGY=90; NGZ=90;! NGXF=32; NGYF=32; NGZF=32

**********************************************************************
POSCAR
**********************************************************************
super cell
3.5100400000
1.915591050311872 0.000000000000000 0.000000000000000
0.000000000000000 1.915591050311872 0.000000000000000
-0.000000000000000 -0.000000000000000 1.915591050311872
16
Selective dynamics
Direct
0.000000000000000 0.000000000000000 0.00000000000000 T T T
0.500000000000000 0.000000000000000 0.00000000000000 T T T
0.000000000000000 0.500000000000000 0.00000000000000 T T T
0.500000000000000 0.500000000000000 0.00000000000000 T T T
0.000000000000000 0.000000000000000 0.50000000000000 T T T
0.500000000000000 0.000000000000000 0.50000000000000 T T T
0.000000000000000 0.500000000000000 0.50000000000000 T T T
0.500000000000000 0.500000000000000 0.50000000000000 T T T
0.250000000000000 0.250000000000000 0.25000000000000 T T T
0.750000000000000 0.250000000000000 0.25000000000000 T T T
0.250000000000000 0.750000000000000 0.25000000000000 T T T
0.750000000000000 0.750000000000000 0.25000000000000 T T T
0.250000000000000 0.250000000000000 0.75000000000000 T T T
0.750000000000000 0.250000000000000 0.75000000000000 T T T
0.250000000000000 0.750000000000000 0.75000000000000 T T T
0.750000000000000 0.750000000000000 0.75000000000000 T T T

*****************************************************************
KPOINTS
*****************************************************************
Automatic mesh
0
Monkhorst Pack
5 5 5
0 0 0


I have the same problem also with other structures. All structures and energies used to perform phonon calculations are correct and in good agreement with literature. All pseudopotentials give the same wrong answer.
Is there any problem with supercell? I think it is large enough to give not so wrong energies...

Please help

[kambiz]

Hi,

let s say you have a surface with an adsorbate on it. To see the frequencies of adsorbate, it s reasonable to fix the surface atoms. So if you need frequencies of all atoms, you should set selective dynamics for each atom as TRUE as you did. But if you need frequencies for some atoms you should set the selective dynamics as "F" for other atoms.

For example:
0.000000000000000 0.000000000000000 0.00000000000000 T T T
0.500000000000000 0.000000000000000 0.00000000000000 T T T
0.000000000000000 0.500000000000000 0.00000000000000 T T T
0.500000000000000 0.500000000000000 0.00000000000000 T T T
0.000000000000000 0.000000000000000 0.50000000000000 T T T
0.500000000000000 0.000000000000000 0.50000000000000 T T T
0.000000000000000 0.500000000000000 0.50000000000000 T T T
0.500000000000000 0.500000000000000 0.50000000000000 T T T
0.250000000000000 0.250000000000000 0.25000000000000 T T T
0.750000000000000 0.250000000000000 0.25000000000000 T T T
0.250000000000000 0.750000000000000 0.25000000000000 F F F
0.750000000000000 0.750000000000000 0.25000000000000 F F F
0.250000000000000 0.250000000000000 0.75000000000000 F F F
0.750000000000000 0.250000000000000 0.75000000000000 F F F
0.250000000000000 0.750000000000000 0.75000000000000 F F F
0.750000000000000 0.750000000000000 0.75000000000000 F F F

Regards

[alex]

Hello nevodo,

why do you think your result is wrong?

Cheers,

alex

[novodo]

Dear kambiz, i tried to select dynamics only for a restricted number of atoms in the cell, but nothing...same problem, same spreading about frequencies. I also tried to change POTIM value, ISYM value (to break down symmetry), but nothing.

**********************************************************************************

Dear alex, in this case I expect just 3 acoustic branches (Li has 1 atom per primitive cell) and so all real frequencies could be 0 at Gamma point.
What do you suggest???


Thanks all

[alex]

Sorry, that's far too much physics language for me. What frequencies do you expect? All zero?

Cheers,

alex

[camilo]

I wouldn't call this a bug.

[yiwang62]

You are fun!

16 atoms - 48 frequencies. Your results are perfectly correct.

If you just want the gamma point phonons, you just need using the primitive 3-atom cells.

If your materials are insulators, you can consider Born effective charge calculation.