non-continuous domain interval for non-bonded interaction in force-matching

[Cecília Álvares]

Hello everyone,

I was wondering if there is a way to  define a "non-continuous" domain interval when setting up the settings.xml file to do force-matching of non-bonded potentials (for example) within VOTCA. I mean, in my case, since I am deriving potentials for a xtalline solid, I have peaks in the RDF that go up and down back to 0 (e.g. below), which would give rise to non-sampled intervals for the potential if I was to use a continuous interval for rij going from the first peak to the last.

[Cecília Álvares]

(I mean, in this case, I could get "chops" of how the potential would look like in different intervals (corresponding to g(r) != 0) and I later can connected the different portions by doing some sort of interpolation myself.)

[Cecília Álvares]

Hmm.. maybe this is actually a very stupid question, because, given that the potential is built by using splines that hold within a small subinterval defined in <step>, I suppose I could get the same result by splitting the ranges of non-zero RDF in different interactions. (it should give the same results, right?)

[Christoph Junghans]

On Wed, May 31, 2023 at 4:27 AM Cecília Álvares
<cecilia...@gmail.com> wrote:
>
> Hmm.. maybe this is actually a very stupid question, because, given that the potential is built by using splines that hold within a small subinterval defined in <step>, I suppose I could get the same result by splitting the ranges of non-zero RDF in different interactions. (it should give the same results, right?)

The reason why we haven't implemented support for non-continuous
domains is mainly that it is complicated to get all the cases right
and so we thought one could just do a piecewise ibi and then combine
it.

Christoph

>
> Em quarta-feira, 31 de maio de 2023 às 12:07:35 UTC+2, Cecília Álvares escreveu:
>>
>> (I mean, in this case, I could get "chops" of how the potential would look like in different intervals (corresponding to g(r) != 0) and I later can connected the different portions by doing some sort of interpolation myself.)
>>
>> Em quarta-feira, 31 de maio de 2023 às 11:54:18 UTC+2, Cecília Álvares escreveu:
>>>
>>> Hello everyone,
>>>
>>> I was wondering if there is a way to define a "non-continuous" domain interval when setting up the settings.xml file to do force-matching of non-bonded potentials (for example) within VOTCA. I mean, in my case, since I am deriving potentials for a xtalline solid, I have peaks in the RDF that go up and down back to 0 (e.g. below), which would give rise to non-sampled intervals for the potential if I was to use a continuous interval for rij going from the first peak to the last.
>>>
>>>

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--
Christoph Junghans
Web: http://www.compphys.de

[Cecília Álvares]

Hey Christoph

You are right, from looking in the literature it does seem complicated.. and my idea of doing some interpolation is not very rightful because by doing that I would be introducing "forces" at given pairwise distances which do not come from predictions from the force matching method. I mean, if the whole purpose is to find a potential that reproduces the forces, I think I would jeopardize the whole thing to one extent or another if my superatoms end up being, even if for a tiny moment, in the artificial repulsive regions I was planning to introduce.

I saw some people who do FM at high temperature in order to get the separate peaks to merge. Seems to have worked for me for the peaks sitting at > 10 angs. And since my first and second peaks in the RDF I showed comes from 1-2 and 1-3 neighbors, I could assign them a separate bonded potential instead. I still have some other problems in the potential I am obtaining but I will figure out :))

Thanks!

Best,

Cecilia