[CP2K-user] [CP2K:19455] Basis Set in Periodic Calculation

[Jürg Hutter]

Hi

the overlap decreases exponentially with distance. CP2K uses a distance
screening to calculate the sums over neighbour cells. The accuracy
can be adapted with EPS_DEFAULT in general or specific for
the integral calculation with EPS_PGF_ORB.

The list of atomic interaction pairs can be printed by

FORCE_EVAL / DFT / PRINT / NEIGHBOR_LISTS
SAB_ORB T

regards
JH

________________________________________
From: 'Maximilian Franz-Xaver Dorfner' via cp2k <cp2k at googlegroups.com>
Sent: Thursday, November 2, 2023 6:43 PM
To: cp2k at googlegroups.com
Subject: Re: [CP2K:19454] Basis Set in Periodic Calculation

Thank you for your quick answer, that ist definitely helpful!

I would have a follow up question to your answer:
How many periodic copies of the unit cell does CP2K take into account resp. how does it determine this number? Or does CP2K compute the overlap matrix in the continuum limit?

Why do I ask these detailed questions: If CP2K does not use the continuum limit (number of unit cells to infinity), then the sum over cell copies in the previously provided manuskript is normalized
by a product of these numbers (xyz dir). For the overlap matrix this scaling factor is important!

Thank you again in advance for your help,
Maximilian Dorfner

Jürg Hutter <hutter at chem.uzh.ch<mailto:hutter at chem.uzh.ch>> schrieb am Do., 2. Nov. 2023, 13:19:
Hi

Yes, you are correct. In order to calculate the overlap matrix at the Gamma point,
you need to accumulate the integrals of all images.

regards
JH

________________________________________
From: 'Maximilian Franz-Xaver Dorfner' via cp2k <cp2k at googlegroups.com<mailto:cp2k at googlegroups.com>>
Sent: Thursday, November 2, 2023 9:44 AM
To: cp2k
Subject: [CP2K:19450] Basis Set in Periodic Calculation

Hi CP2K Developers,
I am currently working on a python3 tool to compute non-adiabatic coupling constants from the CP2K printed Kohn-Sham Hamiltonian and the Overlap Matrices (OLM). To compute this, I have to compute the basis transformation matrix between the atom centered basis at say a geometry 1 and another geometry 2. This is somewhat very similar to computing the overlap matrix. I started with molecules centered in the computational box. Here I can reproduce the OLM from CP2K up to machine precision, if a make the box large enough, and also the coupling constants are very similar to the ones from the literature computed at higher level methods. In this case the basis resembles just a non-periodic GTO as used in many other quantum chemistry packages.
However, strategically I want to extend this to periodic systems. Nonetheless, here I struggle to reproduce the OLM. I wonder, how exactly the periodic basis function in CP2K defined? I assumed that this basis is in terms of a crystalline atomic orbitals (Formula 4 in arxiv manuscript attached). To access the OLM for the periodic system I computed essentially Formula 6 for k=0.

Thank you in advance for your help and best regards,

Maximilian Dorfner

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