Author Topic: General: Aoforce & Numforce  (Read 5342 times)

milianb

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General: Aoforce & Numforce
« on: July 17, 2009, 03:26:07 PM »
Dear all,

I have a very general question concerning the use of aoforce and numforce.

Until now, I was using Aoforce to calculate the vibrational properties of molecules in the ground state, and Numforce for excited states.
Today, trynig to check something, I used Aoforce to calculate the frequencies of an excited state, and I found differences in the results compared to the Numforce calculation: the ordering and the frequencies of the normal modes are different (in same cases, quite different).
It is clear that one performs analytical second derivatives and the other one, numerical, but is that the reason for the big differences? Are there any reasons for using one or the other? In other words, for calculating the frequencies of excited states, which method is more correct?

Thank you,
BegoƱa

Arnim

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Re: General: Aoforce & Numforce
« Reply #1 on: July 20, 2009, 11:08:56 AM »
Hello,

aoforce does not compute second derivatives in excited states.
You were probably comparing ground state with excited state frequencies.

Cheers,
Arnim