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