BRUTEKPOLAR — Use Kurtz’s method for computing nonlinear optical properties in the genuine Cartesian frame.
his keyword activates the polarizability (non-linear optical properties) calculation method contributed by Henry Kurtz. Unlike standard POLAR, however, the polarizabilities are computed in the genuine Cartesian frame. See Chapter 12, Polarizability Methods for a description of this method. The value n.n is the finite field strength and should only be adjusted by experienced users. The default value for n.n is 0.004 au (0.20568 V/cm) and 0.1 au < n.n < 1 × 10-5 au.
APOLAR, KPOLAR, and BRUTEKPOLAR all compute polarizability and hyperpolarizability. Both KPOLAR and BRUTEKPOLAR use the finite difference method of Henry Kurtz to compute these properties. APOLAR instead relies on the analytical gradient of the energy with respect to the an electric field and so is more reliable and less sensitive to the finite field strength. The only difference between KPOLAR and BRUTEKPOLAR is that KPOLAR reports its results in the inertial frame while BRUTEKPOLAR reports its results in the genuine Cartesian frame. APOLAR gives its results in both the inertial frame and the genuine Cartesian frame (at no extra cost). APOLAR is faster than KPOLAR and BRUTEKPOLAR because it relies on analytic gradients.
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