This group governs the dynamical reaction coordinate,
a classical trajectory method based on quantum chemical
potential energy surfaces. In GAMESS these may be either
ab initio or semi-empirical. Because the vibrational
period of a normal mode with frequency 500 wavenumbers is
67 fs, a DRC needs to run for many steps in order to
sample a representative portion of phase space. Almost
all DRCs break molecular symmetry, so build your molecule
with C1 symmetry in $DATA, or specify NOSYM=1 in $CONTRL.
Restart data can be found in the job's OUTPUT file, with
important results summarized to the IRCDATA file.
- NSTEP
- = The number of DRC points to be calculated, not
including the initial point. (default = 1000)
- DELTAT
- = is the time step. (default = 0.1 fs)
- TOTIME
- = total duration of the DRC computed in a previous
job, in fs. The default is the correct value
when initiating a DRC. (default=0.0 fs)
In general, a DRC can be initiated anywhere,
so $DATA might contain coordinates of the
equilibrium geometry, or a nearby transition
state, or something else. You must also
supply an initial kinetic energy, and the
direction of the initial velocity, for which
there are a number of options:
- EKIN
- = The initial kinetic energy (default = 0.0 kcal/mol)
See also ENM, NVEL, and VIBLVL regarding alternate
ways to specify the initial value.
- VEL
- = an array of velocity components, in Bohr/fs.
When NVEL is false, this is simply the direction
of the velocity vector. Its magnitude will be
automatically adjusted to match the desired initial
kinetic energy, and it will be projected so that
the translation of the center of mass is removed.
Give in the order vx1, vy1, vz1, vx2, vy2, ...
- NVEL
- = a flag to compute the initial kinetic energy from
the input VEL using the sum of mass*VEL*VEL/2.
This flag is usually selected only for restarts.
(default=.FALSE.)
The next two allow the kinetic energy to be
partitioned over all normal modes. The
coordinates in $DATA are likely to be from
a stationary point! You must also supply a
$HESS group.
- VIBLVL
- = a flag to turn this option on (default=.FALSE.)
- VIBENG
- = an array of energies (in units of multiples of
the hv of each mode) to be imparted along each
normal mode. The default is to assign the zero
point energy only, VIBENG(1)=0.5, 0.5, ..., 0.5.
If given as a negative number, the initial
direction of the velocity vector is along the
reverse direction of the mode. "Reverse" means
the phase of the normal mode is chosen such that
the largest magnitude component is a negative
value. An example might be VIBENG(4)=2.5 to add
two quanta to mode 4, along with zero point
energy in all modes.
The next three pertain to initiating the DRC
along a single normal mode of vibration. No
kinetic energy is assigned to the other modes.
You must also supply a $HESS group.
- NNM
- = The number of the normal mode to which the initial
kinetic energy is given. The absolute value of NNM
must be in the range 1, 2, ..., 3N-6. If NNM is a
positive/negative value, the initial velocity will
lie in the forward/reverse direction of the mode.
"Forward" means the largest component of the normal
mode is a positive value. (default=0)
- ENM
- = the initial kinetic energy given to mode NNM,
in units of vibrational quanta hv, so the amount
depends on mode NNM's vibrational frequency, v.
If you prefer to impart an arbitrary initial
kinetic energy to mode NNM, specify EKIN instead.
(default = 0.0 quanta)
To summarize, there are five different ways to specify the
DRC trajectory:
- VEL vector with NVEL=.TRUE. This is difficult to
specify at your initial point, and so this option
is mainly used when restarting your trajectory.
The restart information is always in this format.
- VEL vector and EKIN with NVEL=.FALSE. This will
give a desired amount of kinetic energy in the
direction of the velocity vector.
- VIBLVL and VIBENG selected, to give initial kinetic
energy to all of the normal modes.
- NNM and ENM to give quanta to a single normal mode.
- NNM and EKIN to give arbitrary kinetic energy to
a single normal mode.
The most common use of the next two is to
analyze a trajectory with respect to the
minimum energy geometry the trajectory is
traveling around.
- NMANAL
- = a flag to select mapping of the mass-weighted
Cartesian DRC coordinates and velocity (conjugate
momentum) in terms of normal modes step by step.
If you choose this option, you must supply both
C0 and a $HESS group from the stationary point.
(default=.FALSE.)
- C0
- = an array of the coordinates of the stationary
point (the coordinates in $DATA might well be
some other coordinates). Give in the order
x1,y1,z1,x2,y2,...
The next option applies to all input paths which
read a hessian: NMANAL, NNM, or VIBLVL. After
the translations and rotations have been dropped,
the normal modes are renumbered 1, 2, ..., 3N-6.
- HESSTS
- = a flag to say if the hessian corresponds to a
transition state or a minimum. This parameter
controls deletion of the translation and rotation
degrees of freedom, i.e. the default is to drop
the first six "modes", while setting this flag
on drops modes 2 to 7 instead. (default=.FALSE.)
The final variables control the volume of output.
Let F mean the first DRC point found in this run,
and L mean the last DRC point of this run.
- NPRTSM
- = summarize the DRC results every NPRTSM steps,
to the file IRCDATA. (default = 1)
- NPRT=
- 1 Print orbitals at all DRC points
- 0 Print orbitals at F+L (default)
- -1 Never print orbitals
- NPUN =
- 2 Punch all orbitals at all DRC points
- 1 Punch all orbitals at F+L, and occupied
orbitals at DRC points between
- 0 Punch all orbitals at F+L only (default)
- -1 Never punch orbitals