To run a CAC simulation, one may create/modify
cac.in, in which the commands provide all input parameters for a CAC simulation.
cac.in file, along with the potential files (
edens.tab for the EAM potential;
lj.para for the LJ potential), are read by the Fortran CAC code to run the CAC simulation.
The potential files for some FCC metals are provided in the
The EAM formulations for potential energy and the force on atom , , are
The first line of each
*.tab file is
N first_val last_val
N is a positive integer that equals the number of data pair (each line starting from the second line),
last_val are non-negative real numbers suggesting the first and the last datum in the first column (starting from the second line), respectively.
embed.tab, the first column is the unitless host electron energy ; the second column is the embedded energy , in eV.
pair.tab, the first column is the interatomic distance , in Angstrom; the second column is the pair potential , in eV.
edens.tab, the first column is the interatomic distance , in Angstrom; the second column is the unitless local electron density .
For example, the first few lines of
3000 0.5018316703334310 5.995011000293092 0.5018316703334310 8.9800288540000004E-002 0.5036633406668621 9.0604138970000001E-002 0.5054950110002930 9.1404200869999990E-002 0.5073266813337241 9.2200486049999988E-002
In CAC simulations, an approximation is introduced to calculate the host electron density of the integration points in the coarse-grained domain. For more information, read chapter 3 of Shuozhi Xu's Ph.D. dissertation.
The readers may find EAM potential files in these database:
Note that most of these files do not have the format that suits the CAC simulation.
The LJ formulation for potential energy is
where and are two parameters. In the PyCAC code, the interatomic force, not the energy, is shifted such that the force goes continuously to zero at the cut-off distance , i.e., if , ; otherwise, .
lj.para, a blank line or a line with the "#" character in column one (a comment line) is ignored; three positive real numbers (, , and ) and one non-negative real number () are given in any sequence, where is a place holder that should always be 0.0 for the LJ potential. Note that for the EAM potential, equals the minimum interatomic distance, i.e., the smaller
first_val given in
# parameters for the LJ potential epsilon 0.167 sigma 2.315 rcmin 0. rcoff 5.38784
epsilon = ,
sigma = ,
rcmin = , and
rcoff = .
restart_group_number > 0, or
boolean_restart_refine = t and
refine_style = group, one or more
group_in_*.id files need to be provided, where
* is a positive integer. These files are renamed from
group_out_*_#.id files, which are created automatically when the total number of groups > 0. Note that if the
# here does not match that in the
cac_out_#.restart file, the information of the restart group may be incorrect.