zero point energy

Message

minyork · #1 Post by **minyork** » Wed Oct 24, 2007 4:31 pm

Hi everyone,
I am trying to find out Zero point energy.
I calculated vibrational frequencies.
The output looks like:
1 f = 8.061567 THz 50.652321 2PiTHz 268.904932 cm-1 33.339974 meV
/ Y Z dx dy dz
8.977990 6.624706 10.936994 0.006719 0.039428 -0.010154
7.987944 9.674310 9.806018 0.413037 -0.343292 0.197267
9.392611 10.883302 6.807745 -0.085214 -0.018862 0.038322
9.508228 8.622771 5.958509 -0.029949 0.024147 0.006505
8.899424 8.839951 11.853902 -0.042197 0.038273 -0.090672
6.120948 11.197274 9.536179 -0.366692 0.283409 0.284564
7.133821 10.473994 7.537471 0.239226 -0.169573 -0.496675
11.121763 9.271581 11.061170 -0.036620 -0.013825 -0.012190
10.227230 10.075736 8.974636 -0.059553 -0.004650 -0.004309
8.100989 7.451218 8.851565 -0.007203 0.058854 -0.000876
7.236704 8.224175 6.683469 -0.001378 0.084491 0.042668
11.212837 7.045694 10.155996 -0.010302 0.007806 0.001784
10.325511 7.861288 8.082347 -0.020102 0.014122 0.043694

2 f = 7.079362 THz 44.480941 2PiTHz 236.142080 cm-1 29.277897 meV
X Y Z dx dy dz
:
:
:
36 f = 0.013755 THz 0.086428 2PiTHz 0.458831 cm-1 0.056888 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 0.102093 0.019245 0.257813
7.987944 9.674310 9.806018 0.132338 0.029261 0.255157
9.392611 10.883302 6.807745 0.118728 -0.000978 0.240235
9.508228 8.622771 5.958509 0.078889 -0.005243 0.247438
8.899424 8.839951 11.853902 0.139986 0.023439 0.249408
6.120948 11.197274 9.536179 0.154355 0.057985 0.268958
7.133821 10.473994 7.537471 0.119275 0.034302 0.260041
11.121763 9.271581 11.061170 0.139385 -0.010396 0.228982
10.227230 10.075736 8.974636 0.130896 -0.005854 0.233723
8.100989 7.451218 8.851565 0.093099 0.023918 0.263760
7.236704 8.224175 6.683469 0.080405 0.029705 0.270179
11.212837 7.045694 10.155996 0.100642 -0.014724 0.235704
10.325511 7.861288 8.082347 0.091520 -0.010373 0.240363

37 f/i= 0.093217 THz 0.585702 2PiTHz 3.109395 cm-1 0.385516 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 0.239070 0.236352 0.052702
7.987944 9.674310 9.806018 0.199454 0.185082 -0.057749
9.392611 10.883302 6.807745 0.002953 -0.014170 -0.230647
9.508228 8.622771 5.958509 -0.092383 -0.066102 -0.103163
8.899424 8.839951 11.853902 0.331460 0.292073 -0.073353
6.120948 11.197274 9.536179 0.224907 0.223340 -0.011287
7.133821 10.473994 7.537471 0.049036 0.063376 -0.042926
11.121763 9.271581 11.061170 0.280827 0.218279 -0.256222
10.227230 10.075736 8.974636 0.144356 0.105320 -0.241512
8.100989 7.451218 8.851565 0.099915 0.125942 0.067740
7.236704 8.224175 6.683469 -0.046332 0.010972 0.084225
11.212837 7.045694 10.155996 0.189272 0.163435 -0.131329
10.325511 7.861288 8.082347 0.050095 0.050198 -0.115962

38 f/i= 0.154760 THz 0.972383 2PiTHz 5.162226 cm-1 0.640035 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 0.126384 -0.262807 -0.227082
7.987944 9.674310 9.806018 0.139611 -0.145411 0.066515
9.392611 10.883302 6.807745 0.006437 0.053658 0.085192
9.508228 8.622771 5.958509 -0.097969 0.116278 -0.098196
8.899424 8.839951 11.853902 0.232699 -0.333090 -0.049253
6.120948 11.197274 9.536179 0.172332 -0.064649 0.286356
7.133821 10.473994 7.537471 0.035081 0.054700 0.174680
11.121763 9.271581 11.061170 0.199668 -0.327237 -0.136729
10.227230 10.075736 8.974636 0.103914 -0.137326 -0.023564
8.100989 7.451218 8.851565 0.030719 -0.074162 -0.112721
7.236704 8.224175 6.683469 -0.068142 0.117870 -0.003848
11.212837 7.045694 10.155996 0.093973 -0.259108 -0.319251
10.325511 7.861288 8.082347 -0.001108 -0.069287 -0.202501

39 f/i= 0.244434 THz 1.535822 2PiTHz 8.153429 cm-1 1.010897 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 -0.357612 0.051833 0.052647
7.987944 9.674310 9.806018 0.040454 0.150719 -0.026591
9.392611 10.883302 6.807745 0.198217 -0.104919 -0.051938
9.508228 8.622771 5.958509 -0.083284 -0.138854 0.004243
8.899424 8.839951 11.853902 -0.072993 0.084775 -0.003256
6.120948 11.197274 9.536179 0.266850 0.419165 -0.067420
7.133821 10.473994 7.537471 0.144028 0.197717 -0.049322
11.121763 9.271581 11.061170 -0.015325 -0.222980 -0.008401
10.227230 10.075736 8.974636 0.092003 -0.157478 -0.030183
8.100989 7.451218 8.851565 -0.243674 0.111497 0.029157
7.236704 8.224175 6.683469 -0.136336 0.163984 0.006120
11.212837 7.045694 10.155996 -0.301781 -0.259147 0.048161
10.325511 7.861288 8.082347 -0.188592 -0.192250 0.025822

Questions:
1. how to distintiguish rotational and translational from vibrational ones?
Are they the ones with smallest frequencies?

2. In OUTCAR , there are two sets of frequencies:
One set is below:
Eigenvectors and eigenvalues of the dynamical matrix
----------------------------------------------------

the 2nd set is below:
Eigenvectors after division by SQRT(mass)

Eigenvectors and eigenvalues of the dynamical matrix

What is the difference and which one shall we use?

3.
What is the difference between
f= ....
and
f/i = ....

shown as below:
36 f = 0.013755 THz 0.086428 2PiTHz 0.458831 cm-1 0.056888 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 0.102093 0.019245 0.257813
7.987944 9.674310 9.806018 0.132338 0.029261 0.255157
9.392611 10.883302 6.807745 0.118728 -0.000978 0.240235
9.508228 8.622771 5.958509 0.078889 -0.005243 0.247438
8.899424 8.839951 11.853902 0.139986 0.023439 0.249408
6.120948 11.197274 9.536179 0.154355 0.057985 0.268958
7.133821 10.473994 7.537471 0.119275 0.034302 0.260041
11.121763 9.271581 11.061170 0.139385 -0.010396 0.228982
10.227230 10.075736 8.974636 0.130896 -0.005854 0.233723
8.100989 7.451218 8.851565 0.093099 0.023918 0.263760
7.236704 8.224175 6.683469 0.080405 0.029705 0.270179
11.212837 7.045694 10.155996 0.100642 -0.014724 0.235704
10.325511 7.861288 8.082347 0.091520 -0.010373 0.240363

37 f/i= 0.093217 THz 0.585702 2PiTHz 3.109395 cm-1 0.385516 meV
X Y Z dx dy dz
8.977990 6.624706 10.936994 0.239070 0.236352 0.052702
7.987944 9.674310 9.806018 0.199454 0.185082 -0.057749

Thanks,

#2 Post by **admin** » Thu Oct 25, 2007 8:28 am

1) please look at the corresponding eigenvectors of the respective modes to find out the character.
2) the f/i are imaginary frequencies (either due to a translational shift of the unit cell or the complete molecule, or due to the softening of a mode due to phase transition or at a transition state)

minyork · #3 Post by **minyork** » Fri Oct 26, 2007 6:29 pm

Thanks,
There is another problem:
The default value for POTIM is 0.015A.
How to decide the choice of POTIM is proper for a system?
For example, what will the proper choice of POTIM for
transition metals.

tsemi · #4 Post by **tsemi** » Mon Feb 08, 2010 7:20 pm

Hello,

When calculation vibrational frequencies, I get an output similar to the above posted one.

It seems that the vibrational frequency of each atom is listed. How does one extract the vibrational frequency of the system?

Thank you

forsdan · #5 Post by **forsdan** » Mon Feb 08, 2010 7:30 pm

The vibrational frequencies given are the phonon modes at the gamma point. These modes are collective and are not for the individual atoms. Just look at the eigenvectors to confirm this.

What do you mean by that you want to extract the vibration frequency of the system? The frequencies are already given. If you want the zero-point energy just sum up the different energy contribution from all modes. Please elaborate on what you're after.

Best regards,
/Dan