A tensile test is performed with graphene but the fracture strain is so higher than references. The fracture strain in references is below 0.25 strain in the both zigzag and armchair.
I tried to reproduce the results but my simulation is above 0.35 strain.
I’ve seen that this topic is discussed recently but still no conclusion is made. On the discussion the range of cutoff is focused but it seems that the range of cutoff does not affect much on the result, especially in tensile test.
I want to point out there are two cutoffs in airebo potential: one for covalent interaction and the other for LJ term.
According to manual the cutoff for covalent interaction is set to 2 Angstroms. This is defined in ‘CH.airebo’ file and agree with better not to change it.
We can change LJ cutoff on the script. ‘pair_style airebo 2.0’ means LJ cutoff is 2*3.4, namely 6.8 Angstroms. So my understanding is LJ term will be defined between 2 and 6.8 Angstroms.
If this is correct, if I say ‘pair_style airebo 0.5’, LJ cutoff will be 1.7 Angstroms and this is less than 2 Angstroms, which does not make sense but still get the same results with no error.
My first question is what is happening if I set the LJ cutoff less than 2 Angstroms like 0.5 factor(pair_style airebo 0.5).
And the second question is there is any difference between ‘pair_style airebo 1 0 0’ and ‘pair_style airebo 2 0 0’ when LJ term is removed.
A tensile test is performed with graphene but the fracture strain is so
higher than references. The fracture strain in references is below 0.25
strain in the both zigzag and armchair.
I tried to reproduce the results but my simulation is above 0.35 strain.
I've seen that this topic is discussed recently but still no conclusion is
made. On the discussion the range of cutoff is focused but it seems that the
range of cutoff does not affect much on the result, especially in tensile
test.
since you don't provide *any* tangible information about
how you actually implemented your simulation, it is
essentially impossible to make any comments on what
would be causing your problems. my first guess that you
may be loading your system too quickly is therefore
pure speculation. please keep in mind that any help given
can only be as good as the level of information is that
both sides have.
I want to point out there are two cutoffs in airebo potential: one for
covalent interaction and the other for LJ term.
According to manual the cutoff for covalent interaction is set to 2
Angstroms. This is defined in 'CH.airebo' file and agree with better not to
change it.
We can change LJ cutoff on the script. 'pair_style airebo 2.0' means LJ
cutoff is 2*3.4, namely 6.8 Angstroms. So my understanding is LJ term will
be defined between 2 and 6.8 Angstroms.
it is not quite as simple. there is a smooth switching function.
If this is correct, if I say 'pair_style airebo 0.5', LJ cutoff will be 1.7
Angstroms and this is less than 2 Angstroms, which does not make sense but
still get the same results with no error.
My first question is what is happening if I set the LJ cutoff less than 2
Angstroms like 0.5 factor(pair_style airebo 0.5).
this is a speculation that is most easily answered by setting
up a small test calculation with a few atoms and comparing
the resulting energies and forces.
And the second question is there is any difference between 'pair_style
airebo 1 0 0' and 'pair_style airebo 2 0 0' when LJ term is removed.
same answer. you can also try to read the source code, of course.
In the original stand-alone AIREBO code the LJ cutoff is hard-coded as
2.0 * sigma_max**(1/6). Since it is likely never considered, trained
or tested with LJ cutoff less than the REBO max cutoff, it is not a
good idea to do so.
Additionally, in LAMMPS if LJflag is 1 then cutmax is going to be set
to the maximum of 3.0*REBO_cutmax (short-range REBO cutoff), LJmax
(C-C LJ cutoff) and cutLJ*sigma (cutLJ is assigned by the pair_style
command). In any case, you will get a max cutoff larger than REBO
cutoff.
pair_style settings "1 0 0", "2 0 0" and even "0.5 0 0 " have LJflag =
0, hence no matter what the LJ cut is, there is no LJ interaction -
therefore no difference.