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14.4.1 Standard domains

Standard domains are always determined first. They are used to define strong, close, weak, and distant pairs. More accurate results can be obtained with extended domains (see section 14.4.2), but these extensions do not affect the pair classification.

The domains can be determined either by the method of Boughton and Pulay (BP) [J. Comp. Chem. 14, 736 (1993)] or using natural population analysis (NPA) as described in Mol. Phys. 105, 2753 (2007). By default, the BP method is used with PM orbitals, while NPA method is employed with NLMOs. This default behaviour can be superceded using THRBP=value (use the BP method with the given threshold) or NPASEL=value (use the NPA method with the given threshold).

This BP method is somewhat basis set dependent and therefore the default value of THRBP depends on the basis set: 0.980 for AVDZ, 0.985 for AVTZ, and 0.990 for AVQZ. The NPA method is much less basis set dependent and the default value is NPASEL=0.03.

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