forked from lijiext/lammps
pair ufm to pair zbl
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\documentclass[12pt]{article}
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\begin{document}
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$$
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E = -\varepsilon\, \ln{\left[1-\exp{\left(-r^{2}/\sigma^{2}\right)}\right]} \qquad r < r_c
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$$
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$$
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\varepsilon = p\,k_B\,T
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$$
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\end{document}
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\documentclass[12pt]{article}
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\begin{document}
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\begin{eqnarray*}
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U & = & \sum_i^N \sum_{j > i}^N U_{ij}^{(2)} (r_{ij}) +
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\sum_i^N \sum_{j \neq i}^N \sum_{k > j, k \neq i}^N
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U_{ijk}^{(3)} (r_{ij}, r_{ik}, \theta_{ijk})
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\\
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U_{ij}^{(2)} (r) & = & \frac{H_{ij}}{r^{\eta_{ij}}}
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+ \frac{Z_i Z_j}{r}\exp(-r/\lambda_{1,ij})
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- \frac{D_{ij}}{r^4}\exp(-r/\lambda_{4,ij})
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- \frac{W_{ij}}{r^6}, r < r_{c,{ij}}
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\\
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U_{ijk}^{(3)}(r_{ij},r_{ik},\theta_{ijk}) & = & B_{ijk}
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\frac{\left[ \cos \theta_{ijk} - \cos \theta_{0ijk} \right]^2}
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{1+C_{ijk}\left[ \cos \theta_{ijk} - \cos \theta_{0ijk} \right]^2} \times \\
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& & \exp \left( \frac{\gamma_{ij}}{r_{ij} - r_{0,ij}} \right)
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\exp \left( \frac{\gamma_{ik}}{r_{ik} - r_{0,ik}} \right), r_{ij} < r_{0,ij}, r_{ik} < r_{0,ik}
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\end{eqnarray*}
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\end{document}
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\documentclass[12pt]{article}
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\begin{document}
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$$
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E = A \frac{e^{- \kappa r}}{r} \qquad r < r_c
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$$
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\end{document}
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\documentclass[12pt]{article}
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\begin{document}
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$$
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E = \frac{A}{\kappa} e^{- \kappa (r - (r_i + r_j))} \qquad r < r_c
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$$
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\end{document}
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\documentclass[12pt]{article}
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\begin{document}
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\begin{eqnarray*}
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E^{ZBL}_{ij} & = & \frac{1}{4\pi\epsilon_0} \frac{Z_i Z_j \,e^2}{r_{ij}} \phi(r_{ij}/a)+ S(r_{ij})\\
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a & = & \frac{0.46850}{Z_{i}^{0.23} + Z_{j}^{0.23}}\\
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\phi(x) & = & 0.18175e^{-3.19980x} + 0.50986e^{-0.94229x} + 0.28022e^{-0.40290x} + 0.02817e^{-0.20162x}\\
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\end{eqnarray*}
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\end{document}
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@ -42,10 +42,16 @@ Description
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Style *ufm* computes pairwise interactions using the Uhlenbeck-Ford model (UFM) potential :ref:`(Paula Leite2016) <PL2>` which is given by
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.. image:: Eqs/pair_ufm.jpg
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:align: center
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.. math::
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where rc is the cutoff, sigma is a distance-scale and epsilon is an energy-scale, i.e., a product of Boltzmann constant kB, temperature T and the Uhlenbeck-Ford p-parameter which is responsible
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E & = -\varepsilon\, \ln{\left[1-\exp{\left(-r^{2}/\sigma^{2}\right)}\right]} \qquad r < r_c \\
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\varepsilon & = p\,k_B\,T
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where :math:`r_c` is the cutoff, :math:`\sigma` is a distance-scale and
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:math:`\epsilon` is an energy-scale, i.e., a product of Boltzmann constant
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:math:`k_B`, temperature *T* and the Uhlenbeck-Ford p-parameter which
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is responsible
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to control the softness of the interactions :ref:`(Paula Leite2017) <PL1>`.
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This model is useful as a reference system for fluid-phase free-energy calculations :ref:`(Paula Leite2016) <PL2>`.
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@ -55,8 +61,8 @@ or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands, or by mixing as described below:
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* epsilon (energy units)
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* sigma (distance units)
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* :math:`\epsilon` (energy units)
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* :math:`\sigma` (distance units)
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* cutoff (distance units)
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The last coefficient is optional. If not specified, the global *ufm*
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@ -76,7 +82,13 @@ of a run:
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.. note::
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The thermodynamic integration procedure can be performed with this potential using :doc:`fix adapt <fix_adapt>`. This command will rescale the force on each atom by varying a scale variable, which always starts with value 1.0. The syntax is the same described above, however, changing epsilon to scale. A detailed explanation of how to use this command and perform nonequilibrium thermodynamic integration in LAMMPS is given in the paper by :ref:`(Freitas) <Freitas2>`.
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The thermodynamic integration procedure can be performed with this
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potential using :doc:`fix adapt <fix_adapt>`. This command will
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rescale the force on each atom by varying a scale variable, which
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always starts with value 1.0. The syntax is the same described above,
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however, changing epsilon to scale. A detailed explanation of how to
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use this command and perform nonequilibrium thermodynamic integration
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in LAMMPS is given in the paper by :ref:`(Freitas) <Freitas2>`.
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----------
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@ -63,16 +63,21 @@ including SiO2 :ref:`Vashishta1990 <Vashishta1990>`, SiC
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The potential for the energy U of a system of atoms is
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.. image:: Eqs/pair_vashishta.jpg
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:align: center
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.. math::
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U & = \sum_i^N \sum_{j > i}^N U_{ij}^{(2)} (r_{ij}) + \sum_i^N \sum_{j \neq i}^N \sum_{k > j, k \neq i}^N U_{ijk}^{(3)} (r_{ij}, r_{ik}, \theta_{ijk}) \\
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U_{ij}^{(2)} (r) & = \frac{H_{ij}}{r^{\eta_{ij}}} + \frac{Z_i Z_j}{r}\exp(-r/\lambda_{1,ij}) - \frac{D_{ij}}{r^4}\exp(-r/\lambda_{4,ij}) - \frac{W_{ij}}{r^6}, r < r_{c,{ij}} \\
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U_{ijk}^{(3)}(r_{ij},r_{ik},\theta_{ijk}) & = B_{ijk} \frac{\left[ \cos \theta_{ijk} - \cos \theta_{0ijk} \right]^2} {1+C_{ijk}\left[ \cos \theta_{ijk} - \cos \theta_{0ijk} \right]^2} \times \\
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& \exp \left( \frac{\gamma_{ij}}{r_{ij} - r_{0,ij}} \right) \exp \left( \frac{\gamma_{ik}}{r_{ik} - r_{0,ik}} \right), r_{ij} < r_{0,ij}, r_{ik} < r_{0,ik}
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where we follow the notation used in :ref:`Branicio2009 <Branicio2009>`.
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U2 is a two-body term and U3 is a three-body term. The
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:math:`U^2` is a two-body term and U3 is a three-body term. The
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summation over two-body terms is over all neighbors J within
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a cutoff distance = *rc*\ . The twobody terms are shifted and
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a cutoff distance = :math:`r_c`. The twobody terms are shifted and
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tilted by a linear function so that the energy and force are
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both zero at *rc*\ . The summation over three-body terms
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is over all neighbors J and K within a cut-off distance = *r0*\ ,
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both zero at :math:`r_c`. The summation over three-body terms
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is over all neighbors *i* and *k* within a cut-off distance :math:`= r_0`,
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where the exponential screening function becomes zero.
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The *vashishta* style computes these formulas analytically. The
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@ -126,20 +131,20 @@ and three-body coefficients in the formulae above:
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* element 1 (the center atom in a 3-body interaction)
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* element 2
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* element 3
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* H (energy units)
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* eta
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* Zi (electron charge units)
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* Zj (electron charge units)
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* lambda1 (distance units)
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* D (energy units)
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* lambda4 (distance units)
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* W (energy units)
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* rc (distance units)
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* B (energy units)
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* gamma
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* r0 (distance units)
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* C
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* costheta0
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* *H* (energy units)
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* :math:`\eta`
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* :math:`Z_i` (electron charge units)
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* :math:`Z_j` (electron charge units)
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* :math:`\lambda_1` (distance units)
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* *D* (energy units)
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* :math:`\lambda_4` (distance units)
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* *W* (energy units)
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* :math:`r_c` (distance units)
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* *B* (energy units)
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* :math:`\gamma`
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* :math:`r_0` (distance units)
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* *C*
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* :math:`\cos\theta_0`
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The non-annotated parameters are unitless. The Vashishta potential
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file must contain entries for all the elements listed in the
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@ -159,12 +164,14 @@ unambiguous, general, and simple to code, LAMMPS uses a slightly
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confusing method for specifying parameters. All parameters are
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divided into two classes: two-body and three-body. Two-body and
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three-body parameters are handled differently, as described below.
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The two-body parameters are H, eta, lambda1, D, lambda4, W, rc, gamma,
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and r0. They appear in the above formulae with two subscripts. The
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parameters Zi and Zj are also classified as two-body parameters, even
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though they only have 1 subscript. The three-body parameters are B,
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C, costheta0. They appear in the above formulae with three
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subscripts. Two-body and three-body parameters are handled
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The two-body parameters are *H*\ , :math:`\eta`, :math:`\lambda_1`,
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*D*\ , :math:`\lambda_4`, *W*, :math:`r_c`, :math:`\gamma`,
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and :math:`r_0`. They appear in the above formulae with two subscripts.
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The parameters :math:`Z_i` and :math:`Z_j` are also classified
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as two-body parameters, even
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though they only have 1 subscript. The three-body parameters are *B*\ ,
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*C*\ , :math:`\cos\theta_0`. They appear in the above formulae with
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three subscripts. Two-body and three-body parameters are handled
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differently, as described below.
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The first element in each entry is the center atom in a three-body
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@ -184,7 +191,8 @@ ensure that these values are equal. Two-body parameters appearing in
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entries where the 2nd and 3rd elements are different are stored but
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never used. It is good practice to enter zero for these values. Note
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that the three-body function U3 above contains the two-body parameters
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gamma and r0. So U3 for a central C atom bonded to an Si atom and a
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:math:`\gamma` and :math:`r_0`. So U3 for a central C atom bonded to
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an Si atom and a
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second C atom will take three-body parameters from the CSiC entry, but
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two-body parameters from the CCC and CSiSi entries.
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@ -38,10 +38,12 @@ Description
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Style *yukawa* computes pairwise interactions with the formula
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.. image:: Eqs/pair_yukawa.jpg
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:align: center
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.. math::
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Rc is the cutoff.
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E = A \frac{e^{- \kappa r}}{r} \qquad r < r_c
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:math:`r_c` is the cutoff.
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The following coefficients must be defined for each pair of atoms
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types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
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@ -35,11 +35,13 @@ Description
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Style *yukawa/colloid* computes pairwise interactions with the formula
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.. image:: Eqs/pair_yukawa_colloid.jpg
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:align: center
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.. math::
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where Ri and Rj are the radii of the two particles and Rc is the
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cutoff.
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E = \frac{A}{\kappa} e^{- \kappa (r - (r_i + r_j))} \qquad r < r_c
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where :math:`r_i` and :math:`r_j` are the radii of the two particles
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and :math:`r_c` is the cutoff.
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In contrast to :doc:`pair_style yukawa <pair_yukawa>`, this functional
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form arises from the Coulombic interaction between two colloid
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@ -49,7 +51,7 @@ theory. :doc:`Pair\_style yukawa <pair_yukawa>` is a screened Coulombic
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potential between two point-charges and uses no such approximation.
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This potential applies to nearby particle pairs for which the Derjagin
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approximation holds, meaning h << Ri + Rj, where h is the
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approximation holds, meaning :math:`h << r_i + r_j`, where *h* is the
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surface-to-surface separation of the two particles.
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When used in combination with :doc:`pair_style colloid <pair_colloid>`,
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@ -72,17 +74,17 @@ used in :doc:`pair_style yukawa <pair_yukawa>`. For low surface
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potentials, i.e. less than about 25 mV, A can be written as:
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.. parsed-literal::
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.. math::
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A = 2 \* PI \* R\*eps\*eps0 \* kappa \* psi\^2
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A = 2 \pi R\varepsilon\varepsilon_0 \kappa \psi^2
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where
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* R = colloid radius (distance units)
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* eps0 = permittivity of free space (charge\^2/energy/distance units)
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* eps = relative permittivity of fluid medium (dimensionless)
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* kappa = inverse screening length (1/distance units)
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* psi = surface potential (energy/charge units)
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* *R* = colloid radius (distance units)
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* :math:`\varepsilon_0` = permittivity of free space (charge\^2/energy/distance units)
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* :math:`\varepsilon` = relative permittivity of fluid medium (dimensionless)
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* :math:`\kappa` = inverse screening length (1/distance units)
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* :math:`\psi` = surface potential (energy/charge units)
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The last coefficient is optional. If not specified, the global
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yukawa/colloid cutoff is used.
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@ -43,12 +43,16 @@ that ramps the energy, force, and curvature smoothly to zero
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between an inner and outer cutoff. The potential
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energy due to a pair of atoms at a distance r\_ij is given by:
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.. image:: Eqs/pair_zbl.jpg
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:align: center
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.. math::
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where e is the electron charge, epsilon\_0 is the electrical
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permittivity of vacuum, and Z\_i and Z\_j are the nuclear charges of the
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two atoms. The switching function S(r) is identical to that used by
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E^{ZBL}_{ij} & = \frac{1}{4\pi\epsilon_0} \frac{Z_i Z_j \,e^2}{r_{ij}} \phi(r_{ij}/a)+ S(r_{ij})\\
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a & = \frac{0.46850}{Z_{i}^{0.23} + Z_{j}^{0.23}}\\
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\phi(x) & = 0.18175e^{-3.19980x} + 0.50986e^{-0.94229x} + 0.28022e^{-0.40290x} + 0.02817e^{-0.20162x}\\
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where *e* is the electron charge, :math:`\epsilon_0` is the electrical
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permittivity of vacuum, and :math:`Z_i` and :math:`Z_j` are the nuclear
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charges of the
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two atoms. The switching function :math:`S(r)` is identical to that used by
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:doc:`pair_style lj/gromacs <pair_gromacs>`. Here, the inner and outer
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cutoff are the same for all pairs of atom types.
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@ -56,16 +60,17 @@ The following coefficients must be defined for each pair of atom types
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via the :doc:`pair_coeff <pair_coeff>` command as in the examples above,
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or in the LAMMPS data file.
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* Z\_i (atomic number for first atom type, e.g. 13.0 for aluminum)
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* :math:`Z_i` (atomic number for first atom type, e.g. 13.0 for aluminum)
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* Z\_j (ditto for second atom type)
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* :math:`Z_j` (ditto for second atom type)
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The values of Z\_i and Z\_j are normally equal to the atomic
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The values of :math:`Z_i` and :math:`Z_j` are normally equal to the atomic
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numbers of the two atom types. Thus, the user may optionally
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specify only the coefficients for each I==I pair, and rely
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specify only the coefficients for each :math:`i==i` pair, and rely
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on the obvious mixing rule for cross interactions (see below).
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Note that when I==I it is required that Z\_i == Z\_j. When used
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with :doc:`hybrid/overlay <pair_hybrid>` and pairs are assigned
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Note that when :math:`i==i` it is required that :math:`Z_i == Z_j`.
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When used with :doc:`hybrid/overlay <pair_hybrid>` and pairs are
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assigned
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to more than one sub-style, the mixing rule is not used and
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each pair of types interacting with the ZBL sub-style must
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be included in a pair\_coeff command.
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@ -108,9 +113,11 @@ instructions on how to use the accelerated styles effectively.
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, the Z\_i and Z\_j coefficients
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can be mixed by taking Z\_i and Z\_j from the values specified for
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I == I and J == J cases. When used
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For atom type pairs *i,j* and :math:`i \neq i`, the :math:`Z_i` and
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:math:`Z_j` coefficients
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can be mixed by taking :math:`Z_i` and :math:`Z_j` from the values
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specified for
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:math:`i == i` and :math:`j == j` cases. When used
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with :doc:`hybrid/overlay <pair_hybrid>` and pairs are assigned
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to more than one sub-style, the mixing rule is not used and
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each pair of types interacting with the ZBL sub-style
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