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

J. Ye jingyu... at gmail.com
Wed Nov 23 22:40:31 CET 2016


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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