How to obtain accurate frequencies from CP2K? (inside the post the frequencies are compared between CP2K and Gaussian)
jingyu... at gmail.com
Sat Nov 26 22:28:32 CET 2016
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
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:
> you are not consistently running a non-periodic system - you need a
> nonperiodic poisson section too. And
> 1. You have
> 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
> 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
>> 15 modes
>> 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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