Author Topic: Frequency calculation at MP2  (Read 7444 times)

Arrepiadd

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Frequency calculation at MP2
« on: April 06, 2008, 12:59:29 pm »
Hello everyone,

I am a newcomer to Turbomole and just found out tmole and am trying it out. I am more used to programs with a Gaussian style input file so tmole is a big bonus for me.
My first question is do you use frequently the tmole, or you usually go through the define process?

Now, going into my real problem...
In the DOK file (Turbomole 5.10) at page 298 there is an example for calculating the vibrational spectrum at MP2 level.
Just to avoid making everyone going there, the interesting part of it reads like this:
%method
FORCE :: ri-mp2/TZVP [for_nfre=1,gen_symm=c2v]

By looking at what tmole is doing I see several things:
- first, when it goes through the define process it enters the ff and does 20 steps of geometry optimization at the universal force field.
- it then does a dscf, geometry optimization and then calculates the frequencies.

Am I right so far?

Typically this is the right way to go (you optimize the geometry and then calculate the frequencies). But, what if you already have an optimized geometry? If I go through the define process I can just do the regular stuff, in the end I do a dscf and a single point at that geometry and then I can do the Numforce. Is there a similar procedure for tmole?

Sorry for the long post... thank you for you attention if you made it this far.

uwe

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Re: Frequency calculation at MP2
« Reply #1 on: April 07, 2008, 11:28:59 am »
Hi,

FORCE :: ri-mp2/TZVP [for_nfre=1,gen_symm=c2v,gen_spca=1,geo_suff=0]

should do what you want.

gen_spca=1 switches off the geometry optimization (or switches on a single-point calculation),

and

geo_suff=0 switches off the usage of the UFF-hessian for a geometry optimization, so no UFF step will be done.

Regards,

Uwe

Arrepiadd

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Re: Frequency calculation at MP2
« Reply #2 on: April 07, 2008, 01:29:11 pm »
Hello again!

Thanks for the reply!

So, my question is (perhaps it should be directed to the person who made the program):
Why does the default for a frequency calculation go through the process of optimizing (kind of) twice?
Shouldn't that be just left for the GEOMY keyword?

Thanks in advance,
Daniel