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less accuracy until you get the ONE.

However at initial few steps temperature gets too high because of the un-corrected zero point energy, later it gets right if you have right SMASS value.

my question is:

do i need to do zero point energy corrections before i start a NTV kind MD.

thanks for any comments.

There is no zero point energy correction in classical dynamics. By definition, you are treating the nuclei classically.

Also, zero point energy is unrelated to the thermostat. An initial increase in temperature could be due to an unrelaxed initial geometry, but it could not have anything to do with zero point energy

Question 5

Author minyork Post Wed Oct 24 2007, 06:31PM Hi everyone, I am trying to find out zero point energy. Registered Member #862 I calculated vibrational frequencies. Joined Sun Sep 10 The output looks like: 2006, 01:27AM posts 11 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, Back to top admin Thu Oct 25 2007, 10:28AM posts 1833 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) Back to top minyork Fri Oct 26 2007, 08:29PM Thanks, There is another problem: Registered Member #862 The default value for POTIM is 0.015A. Joined: Sun Sep How to decide the choice of POTIM is proper for a system? 10 01:27AM posts 11 Back to top 2006, For example, what will the proper choice of POTIM for transition metals. tsemi Mon Feb 08 2010, 08:20PM Hello, Registered Member #2854 Joined: Mon Mar 09 2009, 02:38PM Location: Golden Colorado USA posts 16 Back to top 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 Mon Feb 08 2010, 08:30PM Registered 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 Member #647 the eigenvectors to confirm this. Joined: Mon Apr 24 11:07AM Location: Gothenburg, Sweden 2006, 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.