<p>set rho0 for the 2nd element to the value 2.25 and set alpha for the
alloy interaction between elements 1 and 2 to 4.37.</p>
<p>The augt1 parameter is related to modifications in the MEAM
formulation of the partial electron density function. In recent
literature, an extra term is included in the expression for the
third-order density in order to make the densities orthogonal (see for
example <aclass="reference internal"href="pair_polymorphic.html#wang"><spanclass="std std-ref">(Wang)</span></a>, equation 3d); this term is included in the
MEAM implementation in lammps. However, in earlier published work
this term was not included when deriving parameters, including most of
those provided in the library.meam file included with lammps, and to
account for this difference the parameter t1 must be augmented by
3/5*t3. If augt1=1, the default, this augmentation is done
automatically. When parameter values are fit using the modified
density function, as in more recent literature, augt1 should be set to
0.</p>
<p>The mixture_ref_t parameter is available to match results with those
of previous versions of lammps (before January 2011). Newer versions
of lammps, by default, use the single-element values of the t
parameters to compute the background reference density. This is the
proper way to compute these parameters. Earlier versions of lammps
used an alloy mixture averaged value of t to compute the background
reference density. Setting mixture_ref_t=1 gives the old behavior.
WARNING: using mixture_ref_t=1 will give results that are demonstrably
incorrect for second-neighbor MEAM, and non-standard for
first-neighbor MEAM; this option is included only for matching with
previous versions of lammps and should be avoided if possible.</p>
<p>The parameters attrac and repuls, along with the integer selection
parameter erose_form, can be used to modify the Rose energy function
used to compute the pair potential. This function gives the energy of
the reference state as a function of interatomic spacing. The form of
this function is:</p>
<preclass="literal-block">
astar = alpha * (r/re - 1.d0)
if erose_form = 0: erose = -Ec*(1+astar+a3*(astar**3)/(r/re))*exp(-astar)
if erose_form = 1: erose = -Ec*(1+astar+(-attrac+repuls/r)*(astar**3))*exp(-astar)
if erose_form = 2: erose = -Ec*(1 +astar + a3*(astar**3))*exp(-astar)
a3 = repuls, astar < 0
a3 = attrac, astar >= 0
</pre>
<p>Most published MEAM parameter sets use the default values attrac=repulse=0.
Setting repuls=attrac=delta corresponds to the form used in several
recent published MEAM parameter sets, such as <aclass="reference internal"href="#valone"><spanclass="std std-ref">(Valone)</span></a></p>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">The default form of the erose expression in LAMMPS was corrected
in March 2009. The current version is correct, but may show different
behavior compared with earlier versions of lammps with the attrac
and/or repuls parameters are non-zero. To obtain the previous default
form, use erose_form = 1 (this form does not seem to appear in the
literature). An alternative form (see e.g. <aclass="reference internal"href="#lee2"><spanclass="std std-ref">(Lee2)</span></a>) is
<p>For atom type pairs I,J and I != J, where types I and J correspond to
two different element types, mixing is performed by LAMMPS with
user-specifiable parameters as described above. You never need to
specify a pair_coeff command with I != J arguments for this style.</p>
<p>This pair style does not support the <aclass="reference internal"href="pair_modify.html"><spanclass="doc">pair_modify</span></a>
shift, table, and tail options.</p>
<p>This pair style does not write its information to <aclass="reference internal"href="restart.html"><spanclass="doc">binary restart files</span></a>, since it is stored in potential files. Thus, you
need to re-specify the pair_style and pair_coeff commands in an input
script that reads a restart file.</p>
<p>This pair style can only be used via the <em>pair</em> keyword of the
<aclass="reference internal"href="run_style.html"><spanclass="doc">run_style respa</span></a> command. It does not support the
<p>This style is part of the MEAM package. It is only enabled if LAMMPS
was built with that package, which also requires the MEAM library be
built and linked with LAMMPS. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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