Can a DynMat calculation for an isolated molecule be done?

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jianmin
Posts: 71
Joined: Fri Jan 15, 2010 2:39 am

Can a DynMat calculation for an isolated molecule be done?

Post by jianmin »

Dear guys,

I need the zero point energy (ZPE) of a gas phase molecule like ethane. My quesitions are:
1. Can we get the vibration frequencies of an isolated molecule in a big box by a Dynamical Matrix calculation?
2. If we can, how do I prepare the DISPLACECAR file? Take ethane (8 atoms) as an example, if I want the displacement to be 0.001, should I just write 8 lines of 0.001, 0.001, 0.001 in the DISPLACECAR file?
3. How do I specify NSW? Is it equal to 3*8+1=25? If I specify NSW to be more than 25, for instance, 30, would I still get the right results?

Thanks a lot.
Last edited by jianmin on Mon Feb 08, 2010 1:51 pm, edited 1 time in total.
graeme
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Re: Can a DynMat calculation for an isolated molecule be done?

Post by graeme »

Yes, that is exactly right. Just make sure to remove the 6 lowest modes (rotation and translation) from the modes.dat file before calculating the zero point energy.

Well, and set NSW correctly; don't make it larger than it should be. It might still work, but the program might also hang.
jianmin
Posts: 71
Joined: Fri Jan 15, 2010 2:39 am

Re: Can a DynMat calculation for an isolated molecule be done?

Post by jianmin »

Prof. Graeme, I appreciate your reply. I will follow your suggestions.
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