[CP2K-user] [CP2K:18226] How to Gaussian type calculations and Performance

DMT dobromirak at gmail.com
Tue Dec 20 13:01:24 UTC 2022


I am new to CP2K and this is my first post in the group. I have heard many 
positive things about the program and I want to study it. First I want to 
learn how to do the kind of calculations I am already used to use other 
software for.

I have several questions and I'm mainly interested in organic systems.

I picked a very simple metalo-organic complex for test of accuracy, 
properties and speed (my resources are not unlimited).

The Gaussian calculation I chose to repeat is very simple - Single Point 
(Energy run) with m062x functional and def2-tzvp basis set. I used the CP2K 
Energy tutorial and managed to put together the attached input file.

To my understanding I have to use QS > METHOD GAPW in order to apply the 
basis set, which I downloaded in CP2K format from the Basis Set Exchange 
web site.
Since the system is not PERIODIC I used POISSON_SOLVER WAVELET.
I also left MIXING T and used BROYDEN_MIXING with ALPHA 0.4 (default) and 
NBROYDEN 8 (from input examples).
I assume in MGRID: NGRIDS 5 and CUTOFF 400 are good values (from other 
In the &XC_FUNCTIONAL I used &HYB_MGGA_X_M06_2X and in the &HF section I 
placed FRACTION 0.54 (54% HF Exchange is the default in m062x).
In the KIND X sections I wrote BASIS_SET def2-tzvp and POTENTIAL ALL, which 
to my understanding forces no core potential at all, but instead uses all 
electrons from the basis. I noticed that in the &DFT section I had to 
place POTENTIAL_FILE_NAME POTENTIAL, because although I'm not using a 
potential CP2K gives an error if I don't provide a potential file. I took 
the file from the "data" dir of the cp2k source code. <<< Is this the 
correct way to do it, when there is no potential ?
My ABC setting in &CELL is 12 12 12, although the system is quite a bit 
smaller in distances between nuclear coordinates - otherwise I get a 
warning about density at the box edges and convergence is even slower.

Are those setting fine, if I simply want to repeat a Gaussian SP job for 
testing ? Have I picked the DFT functional correctly ? How about the HF 
part ? Can you tell me in short what exactly is this MIXING and when to use 
it ?

CP2K performed quite a few times slower than Gaussian (about 10x). I don't 
want to state the exact timings (I checked with the command `time'), 
because Gaussian License prohibits publishing of timing information.
Without the &HF section the performance increases 2x to 3x, but I guess 
that is for the lack of HF Exchange, which simply makes m062x wrong. The 
Energy without HF Ex is considerably higher. Wither way Gaussian gives a 
much lower result for the total Energy. What is going on and am I doing it 
the right way ?

I understand CP2K has its strengths and in no way I want to speak against 
it, I just want to learn how to use it and before I get into PERIODIC 
systems, surface interactions / reactions, solvents and molecular crystals 
(where I bet CP2K is much better than Gaussian) I want to learn the basics 
and repeat the kind of calculations I am used to.

Any comment can be of help. Anything to get to a well done calculation and 
with an increased performance, without sacrificing accuracy too much.

Best Regards,

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