convert pair styles local/density to meam/c

This commit is contained in:
Axel Kohlmeyer
2020-02-24 09:02:16 -05:00
parent 0b10c0ac60
commit d00f8fcd0a
49 changed files with 201 additions and 370 deletions

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\documentstyle[12pt]{article}
\begin{document}
$$
F^{H} = -R_{FU}(U-U^{\infty}) + R_{FE}E^{\infty}
$$
\end{document}

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\documentstyle[12pt]{article}
\begin{document}
$$
-R_{FU}(U-U^{\infty}) = -R_{FE}E^{\infty} - F^{rest}
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
U_{LD} = \sum_i F(\rho_i)
$$
\end{document}
~

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\documentclass[12pt]{article}
\begin{document}
$$
U_{LD} = \sum_k U_{LD}^{(k)} = \sum_i \left[ \sum_k a_\alpha^{(k)} F^{(k)} \left(\rho_i^{(k)}\right) \right]
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
U_{LD} = \sum_i a_\alpha F(\rho_i)
$$
\end{document}

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\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\begin{document}
\[
\varphi(r) =
\begin{cases}
1 & r \le R_1 \\
c_0 + c_2r^2 + c_4r^4 + c_6r^6 & r \in (R_1, R_2) \\
0 & r \ge R_2
\end{cases}
\]
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
\rho_i = \sum_{j \neq i} \varphi(r_{ij})
$$
\end{document}

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\documentstyle[12pt]{article}
\begin{document}
$$
\rho_i^{(k)} = \sum_j b_\beta^{(k)} \varphi^{(k)} (r_{ij})
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
\rho_i = \sum_{j \neq i} b_\beta \varphi(r_{ij})
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
\begin{eqnarray*}
W & = & - a_{sq} | (v_1 - v_2) \bullet \mathbf{nn} |^2 -
a_{sh} | (\omega_1 + \omega_2) \bullet
(\mathbf{I} - \mathbf{nn}) - 2 \Omega_N |^2 - \\
& & a_{pu} | (\omega_1 - \omega_2) \bullet (\mathbf{I} - \mathbf{nn}) |^2 -
a_{tw} | (\omega_1 - \omega_2) \bullet \mathbf{nn} |^2 \qquad r < r_c
\end{eqnarray*}
$$
\Omega_N = \mathbf{n} \times (v_1 - v_2) / r
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
E_{smooth}(r) = E(r)*f(r)
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
\begin{array}{lcl}
f(r) = 1.0 &\mathrm{for}& r < r_m \\
f(r) = (1 - x)^3*(1+3x+6x^2) &\mathrm{for}& r_m < r < r_{cut} \\
f(r) = 0.0 &\mathrm{for}& r >= r_{cut} \\
\end{array}
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
x = \frac{(r-r_m)}{(r_{cut}-r_m)}
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
E(r) = 4\epsilon\Big[\Big(\frac{\sigma}{r}\Big)^{12} - \Big(\frac{\sigma}{r}\Big)^6\Big]
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
E(r) = A e^{(-r/\rho)} -\frac{C}{r^6}
$$
\end{document}

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\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}
$$
E(r) = \frac{A}{r^{12}} - \frac{B}{r^{6}}
$$
\end{document}

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\documentclass[12pt]{article}
\begin{document}
$$
E = \sum_i \left\{ F_i(\bar{\rho}_i)
+ \frac{1}{2} \sum_{i \neq j} \phi_{ij} (r_{ij}) \right\}
$$
\end{document}

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@ -1,14 +0,0 @@
\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
$$
E=\sum_{i<j}\phi(r_{ij})+\sum_{i}U(n_{i}),
$$
$$
n_{i}=\sum_{j}\rho(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f(r_{ij})f(r_{ik})g[\cos(\theta_{jik})]
$$
\end{document}

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\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
$$
E=\sum_{i<j}\phi_{ij}(r_{ij})+\sum_{i}U_i(n_{i}),
$$
$$
n_{i}=\sum_{j\ne i}\rho_j(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f_{j}(r_{ij})f_{k}(r_{ik})g_{jk}[\cos(\theta_{jik})]
$$
\end{document}

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@ -1,23 +0,0 @@
\documentclass[showpacs,amsmath,amssymb,prb]{revtex4}
\usepackage{graphicx}
\usepackage{dcolumn}
\usepackage{bm}
\newcommand{\etal}{{\em et al.}}
\newcommand{\OO}{{\mathcal{O}}}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{eqnarray}
E & = & E_{MEAM} + E_{SW} \nonumber \\
E_{MEAM} & = & \sum _{IJ} \phi (r_{IJ}) + \sum _{I} U(\rho _I) \nonumber \\
E_{SW} & = & \sum _{I} \sum _{JK} F(r_{IJ}) \, F(r_{IK}) \, G(\cos(\theta _{JIK})) \nonumber \\
\rho _I & = & \sum _J \rho(r_{IJ}) + \sum _{JK} f(r_{IJ}) \, f(r_{IK}) \, g(\cos(\theta _{JIK})) \nonumber
\end{eqnarray}
\end{document}

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@ -40,26 +40,35 @@ Description
The *lj/switch3/coulgauss* style evaluates the LJ
vdW potential
.. image:: Eqs/pair_lj_switch3.jpg
:align: center
.. math::
E = 4\epsilon \left[ \left(\frac{\sigma}{r}\right)^{12}-\left(\frac{\sigma}{r}\right)^{6} \right]
, which goes smoothly to zero at the cutoff r\_c as defined
by the switching function
.. image:: Eqs/pair_switch3.jpg
:align: center
.. math::
S_3(r) = \left\lbrace \begin{array}{ll}
1 & \quad\mathrm{if}\quad r < r_\mathrm{c} - w \\
3x^2 - 2x^3 & \quad\mathrm{if}\quad r < r_\mathrm{c} \quad\mathrm{with\quad} x=\frac{r_\mathrm{c} - r}{w} \\
0 & \quad\mathrm{if}\quad r >= r_\mathrm{c}
\end{array} \right.
where w is the width defined in the arguments. This potential
is combined with Coulomb interaction between Gaussian charge densities:
.. image:: Eqs/pair_coulgauss.jpg
:align: center
.. math::
where qi and qj are the
charges on the 2 atoms, epsilon is the dielectric constant which
can be set by the :doc:`dielectric <dielectric>` command, gamma\_i and gamma\_j
are the widths of the Gaussian charge distribution and erf() is the error-function.
This style has to be used in conjunction with the :doc:`kspace_style <kspace_style>` command
E = \frac{q_i q_j \mathrm{erf}\left( r/\sqrt{\gamma_1^2+\gamma_2^2} \right) }{\epsilon r_{ij}}
where :math:`q_i` and :math:`q_j` are the charges on the 2 atoms,
:math:`\epsilon` is the dielectric constant which can be set by the
:doc:`dielectric <dielectric>` command, :math:`\gamma_i` and
:math:`\gamma_j` are the widths of the Gaussian charge distribution and
erf() is the error-function. This style has to be used in conjunction
with the :doc:`kspace_style <kspace_style>` command
If one cutoff is specified it is used for both the vdW and Coulomb
terms. If two cutoffs are specified, the first is used as the cutoff
@ -71,10 +80,9 @@ above, or in the data file or restart files read by the
:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
commands:
* epsilon (energy)
* sigma (distance)
* gamma (distance)
* :math:`\epsilon` (energy)
* :math:`\sigma` (distance)
* :math:`\gamma` (distance)
----------

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@ -62,22 +62,34 @@ upon initialization.
A system of a single atom type (e.g., LJ argon) with a single local density (LD)
potential would have an energy given by:
.. image:: Eqs/pair_local_density_energy.jpg
:align: center
.. math::
where rho\_i is the LD at atom i and F(rho) is similar in spirit to the
embedding function used in EAM potentials. The LD at atom i is given by the sum
U_{LD} = \sum_i F(\rho_i)
.. image:: Eqs/pair_local_density_ld.jpg
:align: center
where phi is an indicator function that is one at r=0 and zero beyond a cutoff
distance R2. The choice of the functional form of phi is somewhat arbitrary,
but the following piecewise cubic function has proven sufficiently general:
:ref:`(Sanyal1) <Sanyal1>`, :ref:`(Sanyal2) <Sanyal2>` :ref:`(Rosenberger) <Rosenberger>`
where :math:`\rho_i` is the LD at atom *i* and :math:`F(\rho)` is
similar in spirit to the embedding function used in EAM potentials. The
LD at atom *i* is given by the sum
.. image:: Eqs/pair_local_density_indicator_func.jpg
:align: center
.. math::
\rho_i = \sum_{j \neq i} \varphi(r_{ij})
where :math:`\varphi` is an indicator function that is one at r=0 and
zero beyond a cutoff distance R2. The choice of the functional form of
:math:`\varphi` is somewhat arbitrary, but the following piecewise cubic
function has proven sufficiently general: :ref:`(Sanyal1) <Sanyal1>`,
:ref:`(Sanyal2) <Sanyal2>` :ref:`(Rosenberger) <Rosenberger>`
.. math::
\varphi(r) =
\begin{cases}
1 & r \le R_1 \\
c_0 + c_2r^2 + c_4r^4 + c_6r^6 & r \in (R_1, R_2) \\
0 & r \ge R_2
\end{cases}
The constants *c* are chosen so that the indicator function smoothly
interpolates between 1 and 0 between the distances R1 and R2, which are
@ -100,34 +112,38 @@ pair style. Please see :ref:`(Sanyal1) <Sanyal1>` for details of the derivation.
The potential is easily generalized to systems involving multiple atom types:
.. image:: Eqs/pair_local_density_energy_multi.jpg
:align: center
.. math::
U_{LD} = \sum_i a_\alpha F(\rho_i)
with the LD expressed as
.. image:: Eqs/pair_local_density_ld_multi.jpg
:align: center
.. math::
where alpha gives the type of atom i, beta the type of atom j, and the
coefficients a and b filter for atom types as specified by the user. a is
called the central atom filter as it determines to which atoms the
potential applies; a\_alpha = 1 if the LD potential applies to atom type alpha
else zero. On the other hand, b is called the neighbor atom filter because it
specifies which atom types to use in the calculation of the LD; b\_beta = 1 if
atom type beta contributes to the LD and zero otherwise.
\rho_i = \sum_{j \neq i} b_\beta \varphi(r_{ij})
where :math:`\alpha` gives the type of atom *i*\ , :math:`\beta` the
type of atom *j*\ , and the coefficients *a* and *b* filter for atom
types as specified by the user. *a* is called the central atom filter as
it determines to which atoms the potential applies; :math:`a_{\alpha} =
1` if the LD potential applies to atom type alpha else zero. On the
other hand, *b* is called the neighbor atom filter because it specifies
which atom types to use in the calculation of the LD; :math:`b_{\beta} =
1` if atom type :math:`\beta` contributes to the LD and zero otherwise.
.. note::
Note that the potentials need not be symmetric with respect to atom types,
which is the reason for two distinct sets of coefficients a and b. An atom type
may contribute to the LD but not the potential, or to the potential but not the
LD. Such decisions are made by the user and should (ideally) be motivated on
physical grounds for the problem at hand.
Note that the potentials need not be symmetric with respect to atom
types, which is the reason for two distinct sets of coefficients *a*
and *b*\ . An atom type may contribute to the LD but not the
potential, or to the potential but not the LD. Such decisions are
made by the user and should (ideally) be motivated on physical
grounds for the problem at hand.
----------
**General form for implementation in LAMMPS:**
Of course, a system with many atom types may have many different possible LD
@ -135,14 +151,18 @@ potentials, each with their own atom type filters, cutoffs, and embedding
functions. The most general form of this potential as implemented in the
pair\_style local/density is:
.. image:: Eqs/pair_local_density_energy_implement.jpg
:align: center
.. math::
where, k is an index that spans the (arbitrary) number of applied LD potentials
N\_LD. Each LD is calculated as before with:
U_{LD} = \sum_k U_{LD}^{(k)} = \sum_i \left[ \sum_k a_\alpha^{(k)} F^{(k)} \left(\rho_i^{(k)}\right) \right]
where, *k* is an index that spans the (arbitrary) number of applied LD
potentials N\_LD. Each LD is calculated as before with:
.. math::
\rho_i^{(k)} = \sum_j b_\beta^{(k)} \varphi^{(k)} (r_{ij})
.. image:: Eqs/pair_local_density_ld_implement.jpg
:align: center
The superscript on the indicator function phi simply indicates that it is
associated with specific values of the cutoff distances R1(k) and R2(k). In
@ -154,10 +174,8 @@ one must specify:
* the neighbor type filter b(k), where k = 1,2,...N\_LD
* the LD potential function F(k)(rho), typically as a table that is later spline-interpolated
----------
**Tabulated input file format:**
@ -189,10 +207,8 @@ Lines 5 to 9+N\_rho constitute the first block. Thus the input file is separated
each specifying its own upper and lower cutoffs, central and neighbor atoms,
and potential. In general, blank lines anywhere are ignored.
----------
**Mixing, shift, table, tail correction, restart, info**\ :
This pair style does not support automatic mixing. For atom type pairs alpha,
beta and alpha != beta, even if LD potentials of type (alpha, alpha) and

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@ -51,8 +51,16 @@ interactions between mono-disperse finite-size spherical particles in
a pairwise fashion. The interactions have 2 components. The first is
Ball-Melrose lubrication terms via the formulas in :ref:`(Ball and Melrose) <Ball1>`
.. image:: Eqs/pair_lubricate.jpg
:align: center
.. math::
W & = - a_{sq} | (v_1 - v_2) \bullet \mathbf{nn} |^2 -
a_{sh} | (\omega_1 + \omega_2) \bullet
(\mathbf{I} - \mathbf{nn}) - 2 \Omega_N |^2 - \\
& a_{pu} | (\omega_1 - \omega_2) \bullet (\mathbf{I} - \mathbf{nn}) |^2 -
a_{tw} | (\omega_1 - \omega_2) \bullet \mathbf{nn} |^2 \qquad r < r_c \\
& \\
\Omega_N & = \mathbf{n} \times (v_1 - v_2) / r
which represents the dissipation W between two nearby particles due to
their relative velocities in the presence of a background solvent with
@ -82,12 +90,14 @@ The other component is due to the Fast Lubrication Dynamics (FLD)
approximation, described in :ref:`(Kumar) <Kumar1>`, which can be
represented by the following equation
.. image:: Eqs/fld.jpg
:align: center
.. math::
F^{H} = -R_{FU}(U-U^{\infty}) + R_{FE}E^{\infty}
where U represents the velocities and angular velocities of the
particles, U\^\ *infty* represents the velocity and the angular velocity
of the undisturbed fluid, and E\^\ *infty* represents the rate of strain
particles, :math:`U^{\infty}` represents the velocity and the angular velocity
of the undisturbed fluid, and :math:`E^{\infty}` represents the rate of strain
tensor of the undisturbed fluid with viscosity *mu*\ . Again, note that
this is dynamic viscosity which has units of mass/distance/time, not
kinematic viscosity. Volume fraction corrections to R\_FU are included

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@ -43,8 +43,16 @@ other types of interactions.
The interactions have 2 components. The first is
Ball-Melrose lubrication terms via the formulas in :ref:`(Ball and Melrose) <Ball2>`
.. image:: Eqs/pair_lubricate.jpg
:align: center
.. math::
W & = - a_{sq} | (v_1 - v_2) \bullet \mathbf{nn} |^2 -
a_{sh} | (\omega_1 + \omega_2) \bullet
(\mathbf{I} - \mathbf{nn}) - 2 \Omega_N |^2 - \\
& a_{pu} | (\omega_1 - \omega_2) \bullet (\mathbf{I} - \mathbf{nn}) |^2 -
a_{tw} | (\omega_1 - \omega_2) \bullet \mathbf{nn} |^2 \qquad r < r_c \\
& \\
\Omega_N & = \mathbf{n} \times (v_1 - v_2) / r
which represents the dissipation W between two nearby particles due to
their relative velocities in the presence of a background solvent with
@ -75,13 +83,15 @@ The other component is due to the Fast Lubrication Dynamics (FLD)
approximation, described in :ref:`(Kumar) <Kumar2>`. The equation being
solved to balance the forces and torques is
.. image:: Eqs/fld2.jpg
:align: center
.. math::
-R_{FU}(U-U^{\infty}) = -R_{FE}E^{\infty} - F^{rest}
where U represents the velocities and angular velocities of the
particles, U\^\ *infty* represents the velocities and the angular
velocities of the undisturbed fluid, and E\^\ *infty* represents the rate
of strain tensor of the undisturbed fluid flow with viscosity
particles, :math:`U^{\infty}` represents the velocities and the angular
velocities of the undisturbed fluid, and :math:`E^{\infty}` represents
the rate of strain tensor of the undisturbed fluid flow with viscosity
*mu*\ . Again, note that this is dynamic viscosity which has units of
mass/distance/time, not kinematic viscosity. Volume fraction
corrections to R\_FU are included if *flagVF* is set to 1 (default).

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@ -60,22 +60,29 @@ Lennard-Jones and Buckingham potential with the addition of a taper
function that ramps the energy and force smoothly to zero between an
inner and outer cutoff.
.. image:: Eqs/pair_mdf-1.jpg
:align: center
.. math::
E_{smooth}(r) = E(r)*f(r)
The tapering, *f(r)*\ , is done by using the Mei, Davenport, Fernando
function :ref:`(Mei) <Mei>`.
.. image:: Eqs/pair_mdf-2.jpg
:align: center
.. math::
f(r) & = 1.0 \qquad \qquad \mathrm{for} \qquad r < r_m \\
f(r) & = (1 - x)^3*(1+3x+6x^2) \quad \mathrm{for} \qquad r_m < r < r_{cut} \\
f(r) & = 0.0 \qquad \qquad \mathrm{for} \qquad r >= r_{cut} \\
where
.. image:: Eqs/pair_mdf-3.jpg
:align: center
.. math::
Here *r\_m* is the inner cutoff radius and *r\_cut* is the outer cutoff
radius.
x = \frac{(r-r_m)}{(r_{cut}-r_m)}
Here :math:`r_m` is the inner cutoff radius and :math:`r_{cut}` is the
outer cutoff radius.
----------
@ -84,48 +91,50 @@ radius.
For the *lj/mdf* pair\_style, the potential energy, *E(r)*\ , is the
standard 12-6 Lennard-Jones written in the epsilon/sigma form:
.. image:: Eqs/pair_mdf-4.jpg
:align: center
.. math::
E(r) = 4\epsilon\biggl[\bigl(\frac{\sigma}{r}\bigr)^{12} - \bigl(\frac{\sigma}{r}\bigr)^6\biggr]
Either the first two or all of the following coefficients must be
defined for each pair of atoms types via the pair\_coeff command as
in the examples above, or in the data file read by the
:doc:`read_data <read_data>`. The two cutoffs default to the global
values and epsilon and sigma can also be determined by mixing as
defined for each pair of atoms types via the pair\_coeff command as in
the examples above, or in the data file read by the :doc:`read_data
<read_data>`. The two cutoffs default to the global values and
:math:`\epsilon` and :math:`\sigma` can also be determined by mixing as
described below:
* epsilon (energy units)
* sigma (distance units)
* r\_m (distance units)
* r\_\ *cut* (distance units)
* :math:`\epsilon` (energy units)
* :math:`\sigma` (distance units)
* :math:`r_m` (distance units)
* :math:`r_{cut}` (distance units)
----------
For the *buck/mdf* pair\_style, the potential energy, *E(r)*\ , is the
standard Buckingham potential with three required coefficients.
The two cutoffs can be omitted and default to the corresponding
global values:
.. image:: Eqs/pair_mdf-5.jpg
:align: center
.. math::
* A (energy units)
* \rho (distance units)
* C (energy-distance\^6 units)
* r\_m (distance units)
* r\_\ *cut* (distance units)
E(r) = A e^{(-r/\rho)} -\frac{C}{r^6}
* *A* (energy units)
* :math:`\rho` (distance units)
* *C* (energy-distance\^6 units)
* :math:`r_m` (distance units)
* :math:`r_{cut}` (distance units)
----------
For the *lennard/mdf* pair\_style, the potential energy, *E(r)*\ , is the
standard 12-6 Lennard-Jones written in the A/B form:
.. image:: Eqs/pair_mdf-6.jpg
:align: center
.. math::
E(r) = \frac{A}{r^{12}} - \frac{B}{r^{6}}
The following coefficients must be defined for each pair of atoms
types via the pair\_coeff command as in the examples above, or in the
@ -133,23 +142,21 @@ data file read by the read\_data commands, or by mixing as described below.
The two cutoffs default to their global values and must be either both
given or both left out:
* A (energy-distance\^12 units)
* B (energy-distance\^6 units)
* r\_m (distance units)
* r\_\ *cut* (distance units)
* *A* (energy-distance\^12 units)
* *B* (energy-distance\^6 units)
* :math:`r_m` (distance units)
* :math:`r_{cut}` (distance units)
----------
**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
For atom type pairs I,J and I != J, the epsilon and sigma coefficients
and cutoff distances for the lj/mdf pair style can be mixed.
The default mix value is *geometric*\ . See the "pair\_modify" command
for details. The other two pair styles buck/mdf and lennard/mdf do not
support mixing, so all I,J pairs of coefficients must be specified
explicitly.
For atom type pairs I,J and I != J, the :math:`\epsilon` and
:math:`sigma` coefficients and cutoff distances for the lj/mdf pair
style can be mixed. The default mix value is *geometric*\ . See the
"pair\_modify" command for details. The other two pair styles buck/mdf
and lennard/mdf do not support mixing, so all I,J pairs of coefficients
must be specified explicitly.
None of the lj/mdf, buck/mdf, or lennard/mdf pair styles supports
the :doc:`pair_modify <pair_modify>` shift option or long-range
@ -161,14 +168,11 @@ to be specified in an input script that reads a restart file.
These styles can only be used via the *pair* keyword of the :doc:`run_style respa <run_style>` command. They do not support the *inner*\ ,
*middle*\ , *outer* keywords.
----------
Restrictions
""""""""""""
These pair styles can only be used if LAMMPS was built with the
USER-MISC package. See the :doc:`Build package <Build_package>` doc
page for more info.

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@ -32,27 +32,31 @@ using a variant of modified embedded-atom method (MEAM) potentials
:ref:`(Lenosky) <Lenosky1>`. For a single species ("old-style") MEAM,
the total energy E is given by
.. image:: Eqs/pair_meam_spline.jpg
:align: center
.. math::
where rho\_i is the density at atom I, theta\_jik is the angle between
atoms J, I, and K centered on atom I. The five functions Phi, U, rho,
f, and g are represented by cubic splines.
E & =\sum_{i<j}\phi(r_{ij})+\sum_{i}U(n_{i}) \\
n_{i} & =\sum_{j}\rho(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f(r_{ij})f(r_{ik})g[\cos(\theta_{jik})]
where :math:`\rho_i` is the density at atom I, :math:`\theta_{jik}` is
the angle between atoms J, I, and K centered on atom I. The five
functions :math:`\phi, U, \rho, f,` and *g* are represented by cubic splines.
The *meam/spline* style also supports a new style multicomponent
modified embedded-atom method (MEAM) potential :ref:`(Zhang) <Zhang4>`, where
the total energy E is given by
.. image:: Eqs/pair_meam_spline_multicomponent.jpg
:align: center
.. math::
where the five functions Phi, U, rho, f, and g depend on the chemistry
of the atoms in the interaction. In particular, if there are N different
chemistries, there are N different U, rho, and f functions, while there
are N(N+1)/2 different Phi and g functions. The new style multicomponent
MEAM potential files are indicated by the second line in the file starts
with "meam/spline" followed by the number of elements and the name of each
element.
E &= \sum_{i<j}\phi_{ij}(r_{ij})+\sum_{i}U_i(n_{i}) \\
n_{i} & = \sum_{j\ne i}\rho_j(r_{ij})+\sum_{\substack{j<k,\\j,k\neq i}}f_{j}(r_{ij})f_{k}(r_{ik})g_{jk}[\cos(\theta_{jik})]
where the five functions :math:`\phi, U, \rho, f,` and *g* depend on the
chemistry of the atoms in the interaction. In particular, if there are
N different chemistries, there are N different *U*\ , :math:`\rho`, and
*f* functions, while there are N(N+1)/2 different :math:`\phi` and *g*
functions. The new style multicomponent MEAM potential files are
indicated by the second line in the file starts with "meam/spline"
followed by the number of elements and the name of each element.
The cutoffs and the coefficients for these spline functions are listed
in a parameter file which is specified by the

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@ -32,12 +32,17 @@ was first proposed by Nicklas, Fellinger, and Park
:ref:`(Nicklas) <Nicklas>`. We refer to it as MEAM+SW. The total energy E
is given by
.. image:: Eqs/pair_meam_sw_spline.jpg
:align: center
.. math::
where rho\_I is the density at atom I, theta\_JIK is the angle between
atoms J, I, and K centered on atom I. The seven functions
Phi, F, G, U, rho, f, and g are represented by cubic splines.
E & = E_{MEAM} + E_{SW} \\
E_{MEAM} & = \sum _{IJ} \phi (r_{IJ}) + \sum _{I} U(\rho _I) \\
E_{SW} & = \sum _{I} \sum _{JK} F(r_{IJ}) \, F(r_{IK}) \, G(\cos(\theta _{JIK})) \\
\rho _I & = \sum _J \rho(r_{IJ}) + \sum _{JK} f(r_{IJ}) \, f(r_{IK}) \, g(\cos(\theta _{JIK}))
where :math:`\rho_I` is the density at atom I, :math:`\theta_{JIK}` is
the angle between atoms J, I, and K centered on atom I. The seven
functions :math:`\phi, F, G, U, \rho, f,` and *g* are represented by
cubic splines.
The cutoffs and the coefficients for these spline functions are listed
in a parameter file which is specified by the

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@ -46,15 +46,18 @@ the 12 December 2018 release.
In the MEAM formulation, the total energy E of a system of atoms is
given by:
.. image:: Eqs/pair_meam.jpg
:align: center
.. math::
where F is the embedding energy which is a function of the atomic
electron density rho, and phi is a pair potential interaction. The
pair interaction is summed over all neighbors J of atom I within the
cutoff distance. As with EAM, the multi-body nature of the MEAM
potential is a result of the embedding energy term. Details of the
computation of the embedding and pair energies, as implemented in
E = \sum_i \left\{ F_i(\bar{\rho}_i)
+ \frac{1}{2} \sum_{i \neq j} \phi_{ij} (r_{ij}) \right\}
where *F* is the embedding energy which is a function of the atomic
electron density :math:`\rho`, and :math:`\phi` is a pair potential
interaction. The pair interaction is summed over all neighbors J of
atom I within the cutoff distance. As with EAM, the multi-body nature
of the MEAM potential is a result of the embedding energy term. Details
of the computation of the embedding and pair energies, as implemented in
LAMMPS, are given in :ref:`(Gullet) <Gullet>` and references therein.
The various parameters in the MEAM formulas are listed in two files

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@ -64,7 +64,7 @@ is combined with Coulomb interaction between Gaussian charge densities:
.. math::
E & = \frac{q_i q_j \mathrm{erf}\left( r/\sqrt{\gamma_1^2+\gamma_2^2} \right) }{\epsilon r_{ij}}
E = \frac{q_i q_j \mathrm{erf}\left( r/\sqrt{\gamma_1^2+\gamma_2^2} \right) }{\epsilon r_{ij}}
where :math:`q_i` and :math:`q_j` are the charges on the 2 atoms,