[CP2K:8433] Re: How to obtain accurate frequencies from CP2K? (inside the post the frequencies are compared between CP2K and Gaussian)

S Ling lingsa... at gmail.com
Thu Nov 24 11:59:42 CET 2016


Hi

In addition to what Matt said, if you really want to compare results from
CP2K and Gaussian, you should: (1) use the all-electron method, i.e. GAPW,
in CP2K; (2) use the same basis sets; (3) use the same method to calculate
frequencies. For (3), Gaussian calculates frequencies analytically by
default, while CP2K calculates frequencies numerically. To calculate
frequencies numerically in Gaussian, you should specify Freq=Numer. And
also the calculated frequencies may be sensitive to the the step size for
numerical differentiation, therefore, you should use the same step size in
both calculations. In Gaussian, this is controlled by the Step keyword, see
http://www.gaussian.com/g_tech/g_ur/k_freq.htm; in CP2K, this is controlled
by the DX keyword.

SL



On 24 November 2016 at 10:05, Matt W <MattWa... at gmail.com> 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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