Field Keyword
Last Update:
12/31/2000
| Description |
The Field keyword requests that a finite field be added to calculation. In Gaussian 98, the field can either involve electric multipoles (through hexadecapoles) or a Fermi contact term. Field requires a parameter in one of these two formats:
M±N or F(M)N
where M designates a multipole, and F(M) designates a Fermi contact perturbation for atom M (following the ordering in the molecule specification section of the input file). N*0.0001 specifies the magnitude of the field in atomic units in the first format, and specifies the magnitude of the Fermi contact perturbation in the second format.
Thus, Field=X+10 applies an electric dipole field in the X direction of 0.001 au, while Field=XXYZ–20 applies the indicated hexadecapole field with magnitude 0.0020 au and direction opposite to the default (which is determined by the standard orientation). Similarly, Field=F(3)27 applies a perturbation of 0.0027 times the spin density on atom 3. Note that the coefficients are those of the Cartesian operator matrices; be careful of the choice of sign convention when interpreting the results.
The field specification parameter may be placed among any other options as desired. Archiving is disabled when Field is specified.
| Options |
Read
Reads the coefficients of all 35 electric
multipole components from the input stream, using format 3D20.10 (The first
component is a charge).
RWF
Takes the 35 multipole components from the
read-write file.
ERWF
Extracts only the three electric dipole field
components from the read-write file.
Checkpoint
Reads the 35 multipole components from the
checkpoint file. Chk is a synonym for Checkpoint.
EChk
Extracts only the three electric dipole field
components from the checkpoint file.
| Availability |
Single point energy, Force, and Scan calculations only.
| Limitations |
Note that if symmetry is left on during a GVB calculation, the finite field will or will not lead to correct numerical derivatives, depending on whether the selected field breaks molecular symmetry. To be safe, use Guess=NoSymm whenever using Field with GVB.