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Calculation With External Electric Fields

Quantum-chemical calculations for molecules in the presence of an external electrical field can be carried out by specifying the extrenal field via


These keywords (the corresponding default values are 0) request an electric field in X, Y, and/or Z direction with a strength of Nx*10**(-6), Ny*10**(-6), and/or Nz*10**(-6) a.u., respectively.


Note that the application of an external electric field might lower the molecular symmetry (e.g., the $C_{2v}$ symmetry of H$_2$O is reduced to $C_s$ when an electric field in $X$ or $Y$ direction is applied). As this lowering is not automatically accounted for, it is strongly recommended to run finite-field calculations with SYM=OFF.

Note that the molecule might be oriented differently depending on the actual symmetry used in the calculation.

Finite-field calculations can be performed with the electric field turned on before the HF-SCF step (default, DIFF_TYPE=RELAXED) or after the HF-SCF step (DIFF_TYPE=UNRELAXED). Both options (which refer to orbital-relaxed and orbital-unrelaxed calculations, respectively) are meaningful in the context of CC theory.

Finite-field calculations are available for the following type of calculations

a) all single-point energy calculations

b) all gradient and first-order property calculations

c) relativistic corrections to the energy

d) polarizability

For all other type of calculations, it is not guaranteed that the electric-field perturbations are correctly considered.


calculations with a finite electric field?

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Page last modified on August 31, 2012, at 08:35 PM
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CFOUR is partially supported by the U.S. National Science Foundation.