atomicrex supports a number of different potential types
that are listed at the end of this section
and described in the following sections.
The potential type(s) are specified in the
<potentials> block of
the main input file. It can be useful to move this block to a separate
file and incorporate it via XML inclusions as
demonstrated in this example. The
comprise several subblocks, which define several different
potentials. It is thereby possible to combine (superimpose) several
potential types. The potential specific blocks share several
id attribute is used to set a unique identifier
for each potential;
species-b identify which
atom types the potential is dealing with. The use
of the attributes is illustrated in the following code segment:
<potentials> <eam id="Al" species-a="Al" species-b="Al"> ... </eam> <eam id="SiAl" species-a="Si" species-b="Al"> ... </eam> <abop id="Si" species-a="Si" species-b="Si"> ... </eam> </potentials>
Each potential is associated with a set of parameters that represent
the degrees of freedom of the potential. The user has to
specify which parameters are allowed to vary during the optimization
process (and are thus “dynamic” DOFs as opposed to “static”
DOFs). This is accomplished by including a
inside the respective potential block that contains a list of
elements named by the parameter they are associated with. These
elements have several attributes:
enabledattribute allows one to switch the DOF from dynamic (
False) to static (
True). This allows one to include or exclude a certain parameter from the fit.
resetattribute specifies whether the DOF is reset to the initial value specified by the user each time a new relaxation round is performed.
maxattributes specify the range, within which the parameter is allowed to vary.
tagattribute is used by some potential forms such as Tersoff and analytic bond-order potentials to associate parameters with certain mixed interactions.
<fit-dof> block could thus look as follows:
<fit-dof> <twomu enabled="True" min="0.1" max="2.0"> <beta enabled="False"> </fit-dof>
More examples can be found in the following sections and in the examples section.
- Lennard-Jones potential
- Embedded atom method potentials
- Tersoff potential
- Analytic bond-order potentials
- Modified embedded atom method
- Tabulated potentials
- Defining functions