double displacement for NumForce

[amavr78]

Hi,
I would like to ask if it is possible to get Numerical Frequencies by doing a double displacement across each direction.
That is, 2 points in negative and 2 points in positive displacement.
I have some rather difficult cases , where the potential energy surface is really flat and as a result I get imaginary frequencies.
However, if i perform analytical frequencies, I don't get any imaginary numbers.
I tried giving a smaller step size, increasing the $scfconv criteria, adding the $denconv and the weight derivatives options in the control, but it did not always help.

The problem is that the system is huge and aoforce takes forever .
I am only interested in the vibrations of my guest molecule, so i can ignore the vibrations from the host material.

Has it been implemented in NumForce ? is there any 'secret' and non-documented keyword ?

any hints are welcome.

Thank you,
Andreas

[uwe]

Hi,

double displacements are not implemented in NumForce. I guess that you use the -frznuclei option which skips the calculation of force constants for frozen coordinates.

A powerful tool for such applications is SNF (http://www.reiher.ethz.ch/software/snf from the group of Markus Reiher. Or their MoViPac (http://www.reiher.ethz.ch/software/movipac) program. Not sure if those programs can also take care of frozen coordinates, but both come along with a nice manual.

Regards,

Uwe

[amavr78]

Thanks a lot Uwe !

This is what I was looking for .