[CP2K-user] [CP2K:18227] Re: How to Gaussian type calculations and Performance

[Marcella Iannuzzi]

Dear Dobomir,

The posted input refers to a pseudo potential calculation using GPW and not 
to an ALL electron calculation using GAPW. 
In this case the total energies of Gaussian and CP2K are not comparable.
But maybe you posted the wrong file. 
Anyway, for molecules please remove the Broyden mixing, which is a G-space 
mixing. 
Concerning the timings, is the single iteration time too long or the number 
of iterations to convergence too large?
In the final timings written in the output it is possible to check which 
part of the calculation is taking large portion of the allocated resources. 

Kind regards
Marcella



On Tuesday, December 20, 2022 at 2:01:25 PM UTC+1 DMT wrote:

> Hello,
>
> 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 have left DIAGONALIZATION ON with ALGORITHM STANDARD.
> 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 
> inputs)
> 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,
> Dobromir
>

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