Merge branch 'master' into doc-continued-refactoring

    message(STATUS "PLUMED download requested - we will build our own")

    include(ExternalProject)

    ExternalProject_Add(plumed_build

      URL https://github.com/plumed/plumed2/releases/download/v2.5.3/plumed-src-2.5.3.tgz

      URL_MD5 de30d6e7c2dcc0973298e24a6da24286

      URL https://github.com/plumed/plumed2/releases/download/v2.6.0/plumed-src-2.6.0.tgz

      URL_MD5 204d2edae58d9b10ba3ad460cad64191

      BUILD_IN_SOURCE 1

      CONFIGURE_COMMAND <SOURCE_DIR>/configure --prefix=<INSTALL_DIR>

                                               ${CONFIGURE_REQUEST_PIC}

Before building LAMMPS with this package, you must first build PLUMED.

PLUMED can be built as part of the LAMMPS build or installed separately

from LAMMPS using the generic `plumed installation instructions <plumedinstall_>`_.

The USER-PLUMED package has been tested to work with Plumed versions

2.4.x, 2.5.x, and 2.6.x and will error out, when trying to run calculations

with a different version of the Plumed kernel.

PLUMED can be linked into MD codes in three different modes: static,

\documentstyle[12pt]{article}

\begin{document}

\[

E = \lambda^n \frac{ C q_i q_j}{\epsilon

\left[ \alpha_{\mathrm{C}} (1-\lambda)^2 + r^2 \right]^{1/2}} \qquad r < r_c

\]

\end{document}