How to obtain accurate frequencies from CP2K? (inside the post the frequencies are compared between CP2K and Gaussian)
J. Ye
jingyu... at gmail.com
Sat Nov 26 22:28:32 CET 2016
Hi Matt,
Thanks very much!. Actually, I found the poisson section will not affect
the total energy of the molecule. I think this is reasonable for small
molecule, but may affect the total energy of the system which is larger. Am
I right?
What does the poisson section do in the calculation?
Thanks very much!
On Thursday, November 24, 2016 at 4:05:55 AM UTC-6, Matt W wrote:
>
> Hi,
>
> you are not consistently running a non-periodic system - you need a
> nonperiodic poisson section too. And
>
> 1. You have
>
> &VIBRATIONAL_ANALYSIS
> DX 1.0E-03
> NPROC_REP 24
> FULLY_PERIODIC TRUE
>
> the fully periodic keyword means that CP2K won't remove rotations (because
> they aren't there for a crystal with pbc) - so you get an extra 3 modes.
>
> 2. You are running a totally different 'model chemistry' in Gaussian
> terminology. You can't compare M062X with PBE directly. PBE (GGAs)
> typically underbind, bonds too long, frequencies too small. M06 maybe is
> better on average.
>
> 3 So you are mixing two things - accurate, i.e. properly performed
> calculation at a given level of theory - and agreement with experiment.
> Changing the model will change the frequencies. Changing settings (CUTOFF
> mainly, probably) will just ensure you get the correct numbers for the
> model. You should run PBE in Gaussian to compare to, if this is what you
> want.
>
> Matt
>
> On Wednesday, November 23, 2016 at 9:40:31 PM UTC, J. Ye wrote:
>>
>> Hi all,
>>
>> I calculate frequency for small molecules and try to compare with
>> Gaussian 09 and experimental results. I show the results from *CP2K *(PBE
>> functional-BASIS_MOPLOT, GTH potental, nonperiodic) and * Gaussian09 *(M062X/6-311g(d,p))
>> .
>>
>> I have several questions:
>>
>> 1. You will see the total number of modes obtained from CP2K is 15,
>> however 12 modes from Gaussian. Are the first three modes are translation
>> modes or rotation modes for C2H4?
>> 2. If we only compare the 12 vibration modes, the value for most of
>> modes from Gaussian is larger than CP2K. What's the reason for getting
>> smaller frequencies from CP2K?
>> 3. What is the keyword can strongly affect the frequencies? Affect the
>> accuracy of frequencies?
>>
>> Thanks very much!
>>
>> CP2K Gaussian
>> c2h4
>> 15 modes
>> -19.0703
>> -5.64472
>> 19.50384
>> 807.9613 831.8134
>> 942.954 988.1607
>> 995.6397 996.8044
>> 1045.988 1071.741
>> 1206.11 1239.784
>> 1373.488 1386.642
>> 1446.925 1470.955
>> 1646.778 1717.766
>> 3158.382 3156.212
>> 3171.654 3172.992
>> 3269.88 3235.274
>> 3270.754 3260.871
>>
>
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