Re: [AMBER] Is Hvib (vibration contribution to enthalpy) considered/calculated in NMA in NAB program?

From: David Case <david.case.rutgers.edu>
Date: Fri, 21 Apr 2017 22:34:03 -0400

On Fri, Apr 21, 2017, Guqin Shi wrote:
>
> Thank you for your reply. I agree that Hvib and Svib are not clearly
> defined here. I learned two terms come from here:
> http://www.colby.edu/chemistry/PChem/notes/NormalModesText.pdf .

This is generally a good exposition, but I must say that I cannot easily
follow what is being argued around Fig. 5. It doesn't seem to be making
conclusions in a context relevant to MM/PBSA calculations. We assume that
the errors arising from using classical mechanics rather than quantum
(nuclear) mechanics cancel in the two end states. But those errors are
sensitive to high-frequency vibrations, not low-frequency ones.

> Are the S and E in nmode() program calculated from the two
> equations above?

See eqs. 35 and 36 in the pdf file referred to above. Those are what is
printed by the nmode() routine.

...dac


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Received on Fri Apr 21 2017 - 20:00:03 PDT
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