Hi Léon
your force field definition is incorrect. The unit for the C parameters should be [kcalmol*angstrom^-6] instead of [kcalmol*angstrom^-1] and the B parameter for Ti-O should be something like 5.15 rather than 0.00515. The simulation cell is also too small for the given RCUT value of 12, but that shouldn’t matter.
HTH
Matthias
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Hi Léon
I think there is no need to use GENPOT, because that nonbonded force field contribution is implemented in CP2K as BUCKMORSE. There are often typos in papers with force field parameters and it is advisable to cross-check the parameter tables for the same force field in different papers for consistency.
Small differences to other codes can have many reasons: splining quality, single- vs double-precision, SPME mesh size, type and threshold values of the employed optimizer etc.
Best
Matthias
From: cp...@googlegroups.com <cp...@googlegroups.com> on behalf of Léon Luntadila Lufungula <Leon.luntad...@uantwerpen.be>
Date: Thursday, 14 March 2024 at 11:48
To: cp2k <cp...@googlegroups.com>
Subject: Re: [CP2K:20027] Matsui-Akaogi Force Field for bulk TiO2
Hi Matthias,
Thanks for pointing this out for me, I've adjusted the input accordingly and now the calculation seems to work fine. I've increased GMAX to 2 points per angstrom and also used MULTIPLE_UNIT_CELL 8 8 3 (each cell
vector should thus be around 30 Angstrom in length), because I read that the cell edge should be at least twice the size of RCUT (i.e., > 24 Angstrom). I tried several versions of the Matsui-Akaogi Force Field to try and get decent values for the cell parameters
after a cell optimization as was shown in their
original paper:
However, no matter which definition I try, I always get cell parameters which are quite a bit larger than those reported and I can't seem to get the original FF definition to work with GENPOT. The parameter sets I tried are attached and labeled as follows:
-
Matsui-Akaogi (MA): original definition with GENPOT [CPASSERT failed]
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Dear Léon
RCUT > L/2 introduces self-interactions, but their effect (as you found) is often negligible.
Best
Matthias
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I had never an issue with that or considered explicitly the actual FFT lengths provided by the employed FFT library. I select values for GMAX appropriate for the actual cell size (e.g. 1 or 2 points per Angstrom). The code should select automatically available FFT lengths equal or larger than the requested values.
Best
Matthias
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