wB97X-V in CP2K

Yuezhi Mao myz... at gmail.com
Sat Jul 14 02:16:50 UTC 2018

Dear CP2K developers,

I was trying to figure out how to run wB97X-V calculations with CP2K, as 
AIMD with this functional using CP2K was reported earlier this year. By 
testing the binding energy for the water dimer in S22 set (the results are 
summarized in the attached .log file), I found the follows:
(i) The setup of this functional in tests/QS/regtest-hybrid-4/wB97X-V.inp 
seems incorrect. The line "FRACTION 0.167" should be deleted. As a mixed 
Coulomb operator is used and the 1/r and erf(wr)/r operators have been 
scaled separately, there is definitely no need to apply an additional 
scaling factor to scale down the exact exchange. From the output generated 
with the same setup as this regtest 
("water_dimer_gapw_wB97X-V_regtest_def2-qzvp.out"), we can find that HF 
exchange energy (as well as the total energy) is particularly small.

(ii) Without the global scaling factor, the total energy given by CP2K 
(using the built-in parameterization) looks too low for this system (the 
corresponding output is "water_dimer_gapw_wB97X-V_regtest_def2-qzvp.out") 
compared to the q-chem reference. It was reported before that wB97X-V, as a 
parameterization of BECKE97, was not implemented correctly because it was 
not attenuated as an SR functional (see a previous discussion on this 
issue: https://groups.google.com/forum/#!msg/cp2k/JEvnnfAEgPY/CFwlbsroSOcJ). 
We suspected that this problem has not been fixed since then.

(iii) Replacing the built-in implementation of the XC functional with the 
counterpart in libxc, the results produced by CP2K (especially the 
GAPW/def2-QZVP calculation) are in great agreement with the Q-Chem numbers. 
Therefore, I believe that the setup in 
"water_dimer_gapw_wB97X-V_def2-qzvp.inp" is the correct way of running this 

I suggest that the regtest job should be modified, as it is often the first 
thing a user would refer to when one wants to try out some new features. 
The current one turns out to be misleading. Also, I think the built-in 
implementation of this functional should be either fixed or disabled, as it 
produces incorrect results.

Best regards,

Yuezhi Mao
Postdoctoral scholar
Department of Chemistry, 
Stanford University
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wB97X-V binding energies:

dimer -34.44798085289274
mon1  -17.21959411186061
mon2  -17.21978344616702
E_int -5.40 kcal/mol

CP2K: GAPW/def2-QZVP (libxc)
dimer -152.91015329020689
mon1  -76.45086050126200
mon2  -76.45089211037026
E_int -5.27 kcal/mol

CP2K: GAPW/def2-QZVP (built-in wB97X-V for XC)
dimer -155.68099539295784
mon1  -77.83866050516080
mon2  -77.83875251157595
E_int -2.25 kcal/mol

CP2K: GAPW/def2-QZVP (regtest setup with FRACTION 0.167)
dimer -151.00306362415915
mon1  -75.50092745482380
mon2  -75.50072244469096
E_int -0.89 kcal/mol

Q-Chem: wB97X-V/def2-QZVP
dimer -152.8884764518
mon1   -76.4400548210
mon2   -76.4400848603
E_int  -5.23 kcal/mol
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