[CP2K-user] [CP2K:20034] Matsui-Akaogi Force Field for bulk TiO2

[Léon Luntadila Lufungula]

P.S. For GMAX it is stated in the manual that "The number of points needs 
to be FFTable (which depends on the library used) and odd for EWALD.", but 
I don't know which numbers are FFTable for FFTW3, could you point me in the 
right direction?

All the best,
Léon
On Friday 15 March 2024 at 11:14:02 UTC+1 Léon Luntadila Lufungula wrote:

> Dear Matthias,
>
> Thanks for pointing me to the right NONBONDED implementation, it seems to 
> work well with BUCKMORSE 
> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/MM/FORCEFIELD/NONBONDED/BUCKMORSE.html>. 
> I also found my error with the other WILLIAMS parameters, I messed up the 
> exponent for the units of C (kcalmol*angstrom^-6 instead of 
> kcalmol*angstrom^6), so now they are working as they should! I was 
> wondering though, how important it is to make sure your cell dimensions are 
> larger than RCUT? I tried redoing the calculation with a 1x1x1 cell instead 
> of 8x8x3 and the results seem to be more or less the same...
>
> Kind regards,
> Léon
>
> On Thursday 14 March 2024 at 20:52:55 UTC+1 Krack Matthias wrote:
>
>> Hi Léon
>>
>>  
>>
>> I think there is no need to use GENPOT, because that nonbonded force 
>> field contribution is implemented in CP2K as BUCKMORSE 
>> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/MM/FORCEFIELD/NONBONDED/BUCKMORSE.html>. 
>> 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... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Léon Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
>> *Date: *Thursday, 14 March 2024 at 11:48
>> *To: *cp2k <cp... at 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 
>> <https://www.tandfonline.com/doi/abs/10.1080/08927029108022432>:
>>
>>  
>>
>> 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) 
>> <https://www.tandfonline.com/doi/abs/10.1080/08927029108022432>: 
>> original definition with GENPOT [CPASSERT failed]
>>
>>
>> - Naicker (N) <https://pubs.acs.org/doi/10.1021/jp050963q>: seemingly 
>> unaltered WILLIAMS version of the original MA definition, although I'm not 
>> 100% sure how to convert the original function into a WILLIAMS type 
>> definition. But f(Bi+Bj) does coincide with rho_ij and Cij coincides with 
>> (Ci+Cj) [a = 3.8865, c = 10.0187]
>>
>> - Predota (P) <https://pubs.acs.org/doi/10.1021/jp037197c>: slightly 
>> altered version to better simulate TiO2 surfaces [a = 3.8865, c = 10.0187]
>>
>> - Alimommadi (A) <https://pubs.acs.org/doi/10.1021/jp207272e>: 
>> parameters should be the same as Predota but are given in eV instead of 
>> kcalmol, but give slightly different result [a = 3.886, c = 10.0177]
>>
>>  
>>
>> Do you know why this could be? Is there still something wrong with my 
>> settings perhaps or should I just accept that the result might not be 
>> ideal? Also, I don't see what I'm doing wrong with the GENPOT definition of 
>> the original MA FF, so any help would be greatly appreciated!
>>
>>  
>>
>> Kind regards,
>>
>> Léon
>>
>> On Wednesday 13 March 2024 at 18:26:08 UTC+1 Krack Matthias wrote:
>>
>> 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: *cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Léon Luntadila Lufungula <Leon.luntad... at uantwerpen.be>
>> *Date: *Wednesday, 13 March 2024 at 12:20
>> *To: *cp2k <cp... 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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