5.4.1 Overview

METHOD
       Specifies the exchange-correlation functional.
TYPE:
       STRING
DEFAULT:
       No default
OPTIONS:
       NAME Use METHOD = NAME, where NAME is either HF for Hartree-Fock theory or else one of the DFT methods listed in Section 5.3.5.
RECOMMENDATION:
       In general, consult the literature to guide your selection. Our recommendations for DFT are indicated in bold in Section 5.3.5.

EXCHANGE
       Specifies the exchange functional (or most exchange-correlation functionals for backwards compatibility).
TYPE:
       STRING
DEFAULT:
       No default
OPTIONS:
       NAME Use EXCHANGE = NAME, where NAME is either: 1) One of the exchange functionals listed in Section 5.3.3 2) One of the XC functionals listed in Section 5.3.5 that is not marked with an asterisk. 3) GEN, for a user-defined functional (see Section 5.3.7).
RECOMMENDATION:
       In general, consult the literature to guide your selection. Our recommendations are indicated in bold in Sections 5.3.5 and  5.3.3.

CORRELATION
       Specifies the correlation functional.
TYPE:
       STRING
DEFAULT:
       NONE
OPTIONS:
       NAME Use CORRELATION = NAME, where NAME is one of the correlation functionals listed in Section 5.3.4.
RECOMMENDATION:
       In general, consult the literature to guide your selection. Our recommendations are indicated in bold in Section 5.3.4.

FAST_XC
       Controls direct variable thresholds to accelerate exchange-correlation (XC) in DFT.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE Turn FAST_XC on. FALSE Do not use FAST_XC.
RECOMMENDATION:
       Caution: FAST_XC improves the speed of a DFT calculation, but may occasionally cause the SCF calculation to diverge.

XC_GRID
       Specifies the type of grid to use for DFT calculations.
TYPE:
       INTEGER
DEFAULT:
       Functional-dependent; see Table 5.3.
OPTIONS:
       0 Use SG-0 for H, C, N, and O; SG-1 for all other atoms. $n$ Use SG-$n$ for all atoms, $n=1,2$, or 3 $XY$ A string of two six-digit integers $X$ and $Y$, where $X$ is the number of radial points and $Y$ is the number of angular points where possible numbers of Lebedev angular points, which must be an allowed value from Table 5.2 in Section 5.5. $-XY$ Similar format for Gauss-Legendre grids, with the six-digit integer $X$ corresponding to the number of radial points and the six-digit integer $Y$ providing the number of Gauss-Legendre angular points, $Y=2N^2$.
RECOMMENDATION:
       Use the default unless numerical integration problems arise. Larger grids may be required for optimization and frequency calculations.

NL_GRID
       Specifies the grid to use for non-local correlation.
TYPE:
       INTEGER
DEFAULT:
       1
OPTIONS:
       Same as for XC_GRID
RECOMMENDATION:
       Use the default unless computational cost becomes prohibitive, in which case SG-0 may be used. XC_GRID should generally be finer than NL_GRID.

XC_SMART_GRID
       Uses SG-0 (where available) for early SCF cycles, and switches to the (larger) target grid specified by XC_GRID for final cycles of the SCF.
TYPE:
       LOGICAL
DEFAULT:
       FALSE
OPTIONS:
       TRUE (or 1) Use the smaller grid for the initial cycles. FALSE (or 0) Use the target grid for all SCF cycles.
RECOMMENDATION:
       The use of the smart grid can save some time on initial SCF cycles.