Dear Users/Developers,
First of all, I think I should start by mentioning that I am a newbie in LAMMPS.
I need a Tersoff style potential for my work.
I tried to use "Brito Mota, J. Appl. Phys., Vol. 86, No. 4, 1999",
however, using those parameters, the Hydrogen on the surface of my
system absurdly "flies away" I have double checked the parameters
against those given in the web page of GULP. Please note that GULP
also complains the system temperature going too high, and when
investigated, it is due to high velocity of hydrogen. Thus I concluded
that this potential is not suitable for the problem at hand.
I am now trying to use the Tersoff potential defined by "T. Ohira,O.
Ukai,M. Noda, Surface Science Volume 458, 2000, Pages 216–228".
However, the functional form has some significant differences.
One of the biggest issues I'm having is the Si-H-H term, where f_R(r)
has to be multiplied by 0.8512 \sum f_c(r) g(\theta). For other
combinations f_R(r) can be used directly.
I was unable to see how this can be done in the already implemented
tersoff pair_style.
Is there an already implemented pair_style or a clever mathematical
trick to bypass this problem?
Best,
Baris
Baris,
No, I don’t see any easy trick to achieving the Ohira form for Si-H-H. To do it, you will have to go in and add some extra code. Once you understand how the existing code works, it should not be too hard to add it in a non-general way for Si-H-H.
Before you invest that effort, you should try to find out if this is really a good potential for your needs. Similarly, before rejecting the Brito potential, you should verify that your LAMMPS parameterization is the same as theirs, by reproducing some of their published results.
Aidan
Dear Aidan,
Thank you very much for the prompt reply.
I am now experimenting to write a tersoff_mod1 pair_style, by copying
and modifying pair_tersoff in MANYBODY package, with the help of the
developer manual.
The developer manual is immensely useful, still I would be very much
glad if there is an example, or some pointers you may want to address
for such an endeavour, for the sake of time I have to invest
understanding the intrinsics of the code.
best wishes,
Baris
You should probably derive from PariTersoff, and not
just copy and re-use a bunch of the existing code.
It may be that you only need to overwrite a method
or two.
Steve
Yes, if you do what Steve says, you will need to know less about "the
intrinsics of the code." I suggest you create a trivial derived class that
only contains a new version of PairTersoff::repulsive() and then build on
that as needed.