How to obtain accurate frequencies from CP2K? (inside the post the frequencies are compared between CP2K and Gaussian)

[J. Ye]

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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