[CP2K-user] [CP2K:20022] Matsui-Akaogi Force Field for bulk TiO2

[Krack Matthias]

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

From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Léon Luntadila Lufungula <Leon.luntadilalufungula at uantwerpen.be>
Date: Wednesday, 13 March 2024 at 12:20
To: cp2k <cp2k at googlegroups.com>
Subject: [CP2K:20022] Matsui-Akaogi Force Field for bulk TiO2
Dear all,

I want to test a force field for TiO2 so that I can use it for pre-equilibrating my system for AIMD calculations. However, I have no experience in using force fields and I'm having trouble implementing the FF calculations. I took the FF parameters from a paper from Naicker et al<https://pubs.acs.org/doi/10.1021/jp050963q> and tried to calculate the energy of the anatase crystal structure, before going on to a cell optimization of the structure to compare to DFT.

However, when I try to run the calculation I get an error indicating "GEOMETRY wrong or EMAX_SPLINE too small!", however, the geometry is definitely correct. So I tried increasing EMAX_SPLINE to 1E2 and then got "SPLINE_INFO| Number of points:  2346797 obtained accuracy 0.953210E-07. MM SPLINE: no convergence on required accuracy (adjust EPS_SPLINE and rerun)". I then tried to increase EPS_SPLINE to 1E-6 and the energy calculation ran without a problem. I tried to run a CELL_OPT with these settings but the optimization seems to be going nowhere... (see attached input and output files) Can anyone tell me what I'm doing wrong? Is it perhaps the definition of the forcefield?

Kind regards,
Léon
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