convert pair styles local/density to meam/c
|
Before Width: | Height: | Size: 3.6 KiB |
@ -1,9 +0,0 @@
|
||||
\documentstyle[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
F^{H} = -R_{FU}(U-U^{\infty}) + R_{FE}E^{\infty}
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 4.1 KiB |
@ -1,9 +0,0 @@
|
||||
\documentstyle[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
-R_{FU}(U-U^{\infty}) = -R_{FE}E^{\infty} - F^{rest}
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 3.0 KiB |
@ -1,11 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
U_{LD} = \sum_i F(\rho_i)
|
||||
$$
|
||||
|
||||
|
||||
\end{document}
|
||||
~
|
||||
|
Before Width: | Height: | Size: 7.8 KiB |
@ -1,9 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 3.4 KiB |
@ -1,9 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
U_{LD} = \sum_i a_\alpha F(\rho_i)
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 8.8 KiB |
@ -1,16 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 3.0 KiB |
@ -1,10 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
|
||||
$$
|
||||
\rho_i = \sum_{j \neq i} \varphi(r_{ij})
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 4.2 KiB |
@ -1,10 +0,0 @@
|
||||
\documentstyle[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
|
||||
$$
|
||||
\rho_i^{(k)} = \sum_j b_\beta^{(k)} \varphi^{(k)} (r_{ij})
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 3.4 KiB |
@ -1,10 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
|
||||
$$
|
||||
\rho_i = \sum_{j \neq i} b_\beta \varphi(r_{ij})
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 14 KiB |
@ -1,17 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 3.1 KiB |
@ -1,9 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
E_{smooth}(r) = E(r)*f(r)
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 9.9 KiB |
@ -1,13 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 2.8 KiB |
@ -1,9 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
x = \frac{(r-r_m)}{(r_{cut}-r_m)}
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 3.8 KiB |
@ -1,9 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 2.6 KiB |
@ -1,9 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
E(r) = A e^{(-r/\rho)} -\frac{C}{r^6}
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 2.5 KiB |
@ -1,9 +0,0 @@
|
||||
\documentclass[12pt]{article}
|
||||
\pagestyle{empty}
|
||||
\begin{document}
|
||||
|
||||
$$
|
||||
E(r) = \frac{A}{r^{12}} - \frac{B}{r^{6}}
|
||||
$$
|
||||
|
||||
\end{document}
|
||||
|
Before Width: | Height: | Size: 6.0 KiB |
@ -1,10 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 21 KiB |
@ -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}
|
||||
|
Before Width: | Height: | Size: 22 KiB |
@ -1,14 +0,0 @@
|
||||
\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}
|
||||
|
Before Width: | Height: | Size: 17 KiB |
@ -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}
|
||||
|
||||
|
||||
@ -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)
|
||||
|
||||
----------
|
||||
|
||||
|
||||
@ -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
|
||||
|
||||
@ -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
|
||||
|
||||
@ -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).
|
||||
|
||||
@ -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.
|
||||
|
||||
@ -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
|
||||
|
||||
@ -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
|
||||
|
||||
@ -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
|
||||
|
||||
@ -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,
|
||||
|
||||