Dear LAMMPS community,
We are interested in using the COMB potential in a system with Ti-Si Ti-O
and Si-O interactions and on top of that using it as a part of a hybrid. I
have two questions regarding this (I'm not sure if it's here that I should
post the first one, please feel free to just ignore it and direct me to the
right person for this) :
1) We have very nearly succeeded in generating the new lines to be added to
the parameter file ffield.comb but the few parameters whose usage we
haven't been able to deduce from the 4 or 5 published papers on the subject
are : A123, Aconf and R_omega_{a,b,c,d}. On
http://lammps.sandia.gov/doc/pair_comb.html
A123 is defined as the equilibrium O-M-O or M-O-M bond angle. Does this
mean that for a triplet like, say, Si-Si-Ti, it is not defined or that it's
just a typo and I should find out the eqm angle for ANY triplet using DFT
or such? The same goes also for Aconf.
As far as R_omega_{a,b,c,d} are concerned, it would be sufficient for me to
make sure that they (like all parameters unless otherwise stated) refer to
element 1.
Once we've successfully made this addition and tested it, I'll be happy to
commit.
2) I believe that as of the 16/Aug built, there seems to be a slight
problem with the usage of the COMB potential as a part of a hybrid. To
illustrate this, when I run the HfO2 example provided in the examples/
folder, it runs fine. When I add a fictitious third species (a single
proton) that is supposed to interact with everyone else through coul/cut, I
get the following error :
ERROR: Pair coeff for hybrid has invalid style (pair_hybrid.cpp:330)
I am attaching the input, data file and the log file. We have tried several
variations of this and COMB doesn't seem to like being in a hybrid
situation. A cursory look at the suggested code snippet
int none = 0;
if (m == nstyles) {
if (strcmp(arg[2],"none") == 0) none = 1;
else error->all(FLERR,"Pair coeff for hybrid has invalid style");
and around it seems to suggest (I'm only guessing) that maybe comb is not a
defined keyword for the hybrid style? More likely of course, it's our
mistake and we have looked through the documentation to single out any
possible clashes but probably missed something. Has anyone been able to use
comb as a part of a hybrid? If yes, I would love to take a look at their
input or be grateful if they pointed out the mistake.
Many thanks in advance and apologies for the lengthy message.
Best wishes,
Hande Toffoli
in.comb.HfO2-hybrid (1.25 KB)
data.m-HfO2-hybrid (103 KB)
log.lammps (767 Bytes)