Keyword AUGMENT

This keyword specifies the basis set augmentation in XAS calculations.
Options:

$<$Augment$>$

The basis set augmentation string $<$Augment$>$ defines the global augmentation basis set. By default, no augmentation is performed.

As for the orbital basis set options, the XAS (see 4.8.7) augmentation basis set can be assigned to individual atoms by the atomic symbol or to atom groups by the element symbol in the keyword block of AUGMENT. The syntax and hierarchy of these assignments is analogous to the orbital basis set assignments (see 4.3.1). Thus, the following input sequence

 AUGMENT (XAS-I)
 S       (XAS-II)

requests the XAS-I augmentation basis set for all atoms, except sulfur, for which the XAS-II augmentation basis set is used. These are the two augmentation basis sets available in the deMon2k basis set file. XAS-I is typically used for first-row atoms whereas XAS-II is somewhat more extended and, therefore, appropriate for heavier atoms. Note that for reliable XAS spectra the augmentation basis is needed, at least on the core-excited atom. Otherwise the sampling of the continuum and Rydberg states will be too coarse. Augmentation basis sets can also be defined directly in the input file using the format:

 Augment
 SYMBOL Read
 N  L  K
    EXPONENT  COEFFICIENT
       :          :
    EXPONENT  COEFFICIENT

The syntax is the same as for the reading of basis sets.