$DRC

$DRC group (relevant for RUNTYP=DRC)

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:

  1. 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.
  2. VEL vector and EKIN with NVEL=.FALSE. This will give a desired amount of kinetic energy in the direction of the velocity vector.
  3. VIBLVL and VIBENG selected, to give initial kinetic energy to all of the normal modes.
  4. NNM and ENM to give quanta to a single normal mode.
  5. 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



References:

J.J.P.Stewart, L.P.Davis, L.W.Burggraf, J.Comput.Chem. 8, 1117-1123 (1987)

S.A.Maluendes, M.Dupuis, J.Chem.Phys. 93, 5902-5911(1990)

T.Taketsugu, M.S.Gordon, J.Phys.Chem. 99, 8462-8471(1995)

T.Taketsugu, M.S.Gordon, J.Phys.Chem. 99, 14597-604(1995)

T.Taketsugu, M.S.Gordon, J.Chem.Phys. 103, 10042-9(1995)

T.Taketsugu, M.S.Gordon, J.Chem.Phys. 104, 2834-40(1996)

M.S.Gordon, G.Chaban, T.Taketsugu J.Phys.Chem. 100, 11512-11525(1996)

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