mirror of
https://github.com/nwchemgit/nwchem.git
synced 2026-07-28 14:15:30 -04:00
97f303e6f8
automatically be expanded to include useful information about the checkin (including the file's revision number). With the switch over to SVN this was lost because SVN only does this expansion if you explicitly ask for it (for every single file). I have added a script to the contrib directory that sets the appropriate property to get SVN to do this expansion. This script will make it easy to do this every time new source files are added. It is called svn_expand_Id, the script contains some comments that explain the issue and how it addresses this. This checkin sets this property for a subset of the relevant files (trying to commit all files at once failed with svn crashing). In future the script will only affect those files for which the property was not set before.
161 lines
4.2 KiB
TeX
161 lines
4.2 KiB
TeX
%
|
|
% $Id$
|
|
%
|
|
\label{sec:mepgs}
|
|
|
|
|
|
The MEPGS module performs a search for the two critical points on the
|
|
potential energy surface connected to a saddle point of the molecule
|
|
defined by input using the \verb+GEOMETRY+ directive (see Section \ref{sec:geom}).
|
|
The algorithm programmed in MEPGS is a {\bf constrained} trust region quasi-newton optimization and approximate energy Hessian updates.
|
|
|
|
|
|
Optional input for this module is specified within the compound
|
|
directive,
|
|
\begin{verbatim}
|
|
MEPGS
|
|
|
|
OPTTOL <real opttol default 3e-4>
|
|
|
|
EPREC <real eprec default 1e-7>
|
|
|
|
STRIDE <real stride default 0.1>
|
|
|
|
EVIB <real evib default 1e-4>
|
|
|
|
MAXMEP <integer maxiter default 250>
|
|
|
|
MAXITER <integer maxiter default 20>
|
|
|
|
INHESS <integer inhess default 2>
|
|
|
|
(BACKWARD || FORWARD) <string default both>
|
|
|
|
(MSWG || NOMSWG) <string default NOMSWG>
|
|
|
|
(XYZ || NOXYZ)
|
|
|
|
END
|
|
\end{verbatim}
|
|
|
|
\sloppy
|
|
|
|
\section{Convergence criteria}
|
|
|
|
The user may request a specific value for the tolerance with the keyword \verb+OPTTOL+ which will couple all the convergence criteria in the following way:
|
|
|
|
\begin{verbatim}
|
|
GRMS 1.0*OPTTOL
|
|
GMAX 1.5*OPTTOL
|
|
XRMS 4.0*OPTTOL
|
|
XMAX 6.0*OPTTOL
|
|
\end{verbatim}
|
|
|
|
\section{Available precision}
|
|
|
|
\begin{verbatim}
|
|
EPREC <real eprec default 1e-7>
|
|
\end{verbatim}
|
|
|
|
In performing a constrained trust region optimization the precision of the energy is coupled to the convergence criteria (see Section \ref{sec:tropt:eprec}).
|
|
Note that the default EPREC for DFT calculations is 5e-6 instead of 1e-7.
|
|
|
|
\section{Controlling the step length}
|
|
|
|
\begin{verbatim}
|
|
STRIDE <real stride default 0.1>
|
|
\end{verbatim}
|
|
|
|
A dynamic stride (\verb+stride+) is used to control the step length during
|
|
the minimum energy path walking when taking the Euler step as starting point.
|
|
|
|
\section{Moving away from the saddle point}
|
|
|
|
\begin{verbatim}
|
|
EVIB <real evib default 1e-4>
|
|
\end{verbatim}
|
|
|
|
The expected decrease in energy (\verb+evib+) assuming a quadratic approximation around the saddle structure to be obtained.
|
|
|
|
\section{Maximum number of MEPGS steps}
|
|
|
|
\begin{verbatim}
|
|
MAXMEP <integer maxmep default 250>
|
|
\end{verbatim}
|
|
|
|
By default at most 250 minimum energy path steps will be taken,
|
|
but this may be modified with this directive.
|
|
|
|
\section{Maximum number of steps}
|
|
|
|
\begin{verbatim}
|
|
MAXITER <integer maxiter default 20>
|
|
\end{verbatim}
|
|
|
|
By default at most 20 {\bf constrained} geometry optimization steps will be taken,
|
|
but this may be modified with this directive.
|
|
|
|
\section{Initial Hessian}
|
|
\begin{verbatim}
|
|
INHESS <integer inhess default 2>
|
|
\end{verbatim}
|
|
|
|
With this option the MEPGS module will be able to transform
|
|
Cartesian Hessian from previous frequency calculation.
|
|
|
|
\section{Selecting the side to traverse}
|
|
\begin{verbatim}
|
|
(BACKWARD || FORWARD) <string default both>
|
|
\end{verbatim}
|
|
|
|
With this option the MEPGS module will select which side of the
|
|
minimum energy path to explore. By default both sides are explored
|
|
for a MEPGS run.
|
|
|
|
\section{Using mass}
|
|
\begin{verbatim}
|
|
(MSWG || NOMSWG) <string default NOMSWG>
|
|
\end{verbatim}
|
|
|
|
With this option the MEPGS will trigger the use of mass when following the
|
|
minimum energy path. Mass is not used as default, if mass is used then
|
|
this formally becomes an intrinsic reaction coordinate.
|
|
|
|
\section{Minimum energy path saved XYZ file}
|
|
|
|
\begin{verbatim}
|
|
XYZ [<string xyz default $fileprefix>]
|
|
NOXYZ
|
|
\end{verbatim}
|
|
|
|
The \verb+XYZ+ directive causes the geometry at each calculated
|
|
structure on the minimum energy path to be output into file in the
|
|
permanent directory in XYZ format.
|
|
The optional string will
|
|
prefix the filename. The \verb+NOXYZ+ directive turns this off.
|
|
|
|
For example, the input
|
|
\begin{verbatim}
|
|
mepgs; xyz ; end
|
|
\end{verbatim}
|
|
will cause a trajectory file filename.xyz to be created
|
|
in the permanent directory.
|
|
|
|
\section{MEPGS usage}
|
|
|
|
\begin{verbatim}
|
|
start somename
|
|
geometry; <saddle point body > ; end
|
|
task theory freq
|
|
freq; reuse somename.hess ; end
|
|
mepgs; <mepgs options> ; end
|
|
task theory mepgs
|
|
\end{verbatim}
|
|
|
|
In the above example, after performing a frequency analysis for the saddle
|
|
point, the information of the force constant matrix is reused (freq directive)
|
|
in order to be able to follow the transition state mode.
|
|
|
|
\fussy
|
|
|
|
|