The DRIVER module is one of two drivers (see Section 22
for documentation on STEPPER) to perform a geometry optimization
function on the molecule defined by input using the GEOMETRY
directive (see Section 6). Geometry optimization is
either an energy minimization or a transition state optimization.
The algorithm programmed in DRIVER is a quasi-newton optimization
with line searches and approximate energy Hessian updates.
DRIVER is selected by default out of the two available modules to perform geometry optimization. In order to force use of DRIVER (e.g., because a previous optimization used STEPPER) provide a DRIVER input block (below) -- even an empty block will force use of DRIVER.
Optional input for this module is specified within the compound directive,
DRIVER
(LOOSE || DEFAULT || TIGHT)
GMAX <real value>
GRMS <real value>
XMAX <real value>
XRMS <real value>
EPREC <real eprec default 1e-7>
TRUST <real trust default 0.3>
SADSTP <real sadstp default 0.1>
CLEAR
REDOAUTOZ
INHESS <integer inhess default 0>
(MODDIR || VARDIR) <integer dir default 0>
(FIRSTNEG || NOFIRSTNEG)
MAXITER <integer maxiter default 20>
BSCALE <real BSCALE default 1.0>
ASCALE <real ASCALE default 0.25>
TSCALE <real TSCALE default 0.1>
HSCALE <real HSCALE default 1.0>
PRINT ...
XYZ [<string xyz default $file_prefix$>]
NOXYZ
END
(LOOSE || DEFAULT || TIGHT)
GMAX <real value>
GRMS <real value>
XMAX <real value>
XRMS <real value>
In version 3.3 Gaussian-style convergence criteria have been adopted.
The defaults may be used, or the directives LOOSE,
DEFAULT, or TIGHT specified to use standard sets of
values, or the individual criteria adjusted. All criteria are in
atomic units.
GMAX and GRMS control the maximum and root mean square
gradient in the coordinates being used (Z-matrix, redundant internals,
or Cartesian). XMAX and XRMS control the maximum and
root mean square of the Cartesian step.
LOOSE DEFAULT TIGHT
GMAX 0.0045d0 0.00045 0.000015
GRMS 0.0030d0 0.00030 0.00001
XMAX 0.0054d0 0.00180 0.00006
XRMS 0.0036d0 0.00120 0.00004
Note that GMAX and GRMS used for convergence of geometry may significantly vary in different coordinate systems such as Z-matrix, redundant internals, or Cartesian. The coordinate system is defined in the input file (default is Z-matrix). Therefore the choice of coordinate system may slightly affect converged energy. Although in most cases XMAX and XRMS are last to converge which are always done in Cartesian coordinates, which insures convergence to the same geometry in different coordinate systems.
The old criterion may be recovered with the input
gmax 0.0008; grms 1; xrms 1; xmax 1
EPREC <real eprec default 1e-7>
In performing a line search the optimizer must know the precision of the energy (this has nothing to do with convergence criteria). The default value of 1e-7 should be adjusted if less, or more, precision is available. Note that the default EPREC for DFT calculations is 5e-6 instead of 1e-7.
TRUST <real trust default 0.3>
SADSTP <real sadstp default 0.1>
A fixed trust radius (trust) is used to control the step during
minimizations, and is also used for modes being minimized during
saddle-point searches. It defaults to 0.3 for minimizations and 0.1
for saddle-point searches. The parameter sadstp is the trust
radius used for the mode being maximized during a saddle-point search
and defaults to 0.1.
MAXITER <integer maxiter default 20>
By default at most 20 geometry optimization steps will be taken, but this may be modified with this directive.
CLEAR
By default Driver reuses Hessian information from a previous optimization, and, to facilitate a restart also stores which mode is being followed for a saddle-point search. This option deletes all restart data.
REDOAUTOZ
Deletes Hessian data and regenerates internal coordinates at the current geometry. Useful if there has been a large change in the geometry that has rendered the current set of coordinates invalid or non-optimal.
INHESS <integer inhess default 0>
In addition, the diagonal elements of the initial Hessian for internal coordinates may be scaled using separate factors for bonds, angles and torsions with the following
BSCALE <real bscale default 1.0>
ASCALE <real ascale default 0.25>
TSCALE <real tscale default 0.1>
These values typically give a two-fold speedup over unit values, based
on about 100 test cases up to 15 atoms using 3-21g and 6-31g* SCF.
However, if doing many optimizations on physically similar systems it
may be worth fine tuning these parameters.
Finally, the entire Hessian from any source may be scaled by a factor using the directive
HSCALE <real hscale default 1.0>
It might be of utility, for instance, when computing an initial
Hessian using SCF to start a large MP2 optimization. The SCF
vibrational modes are expected to be stiffer than the MP2, so scaling
the initial Hessian by a number less than one might be beneficial.
(MODDIR || VARDIR) <integer dir default 0>
(FIRSTNEG || NOFIRSTNEG)
When searching for a transition state the program, by default, will take an initial step uphill and then do mode following using a fuzzy maximum overlap (the lowest eigen-mode with an overlap with the previous search direction of 0.7 times the maximum overlap is selected). Once a negative eigen-value is found, that mode is followed regardless of overlap.
The initial uphill step is appropriate if the gradient points roughly
in the direction of the saddle point, such as might be the case if a
constrained optimization was performed at the starting geometry.
Alternatively, the initial search direction may be chosen to be along
a specific internal variable (using the directive
VARDIR) or along a specific eigen-mode (using MODDIR).
Following a variable might be valuable if the initial gradient is
either very small or very large. Note that the eigen-modes in the
optimizer have next-to-nothing to do with the output from a frequency
calculation. You can examine the eigen-modes used by the optimizer
with
driver; print hvecs; end
The selection of the first negative mode is usually a good choice if
the search is started in the vicinity of the transition state and the
initial search direction is satisfactory. However, sometimes the
first negative mode might not be the one of interest (e.g., transverse
to the reaction direction). If NOFIRSTNEG is specified, the
code will not take the first negative direction and will continue doing
mode-following until that mode goes negative.
XYZ [<string xyz default $fileprefix>]
NOXYZ
The XYZ directive causes the geometry at each step (but not
intermediate points of a line search) to be output into separate files
in the permanent directory in XYZ format. The optional string will
prefix the filename. The NOXYZ directive turns this off.
For example, the input
driver; xyz test; end
will cause files test-000.xyz, test-001.xyz, ... to be created
in the permanent directory.
The script rasmolmovie in the NWChem contrib directory
can be used to turn these into an animated GIF movie.
The UNIX command "egrep '^@' < output" will extract a pretty
table summarizing the optimization.
If you specify the NWChem input
scf; print none; end
driver; print low; end
task scf optimize
you'll obtain a pleasantly terse output.
For more control, these options for the standard print directive are recognized
debug - prints a large amount of data. Don't use in parallel.
high - print the search direction in internals
default - prints geometry for each major step (not during
the line search), gradient in internals (before
and after application of constraints)
low - prints convergence and energy information. At
convergence prints final geometry, change in internals
from initial geometry