# EXCHANGE

Setup parameters for the evaluation of the EXCHANGE and core Hamiltonian terms in SE calculations. [Edit on GitHub]

## Keywords

- CUTOFF

- RC_RANGE

- RC_TAPER

## Keyword descriptions

CUTOFF: real = 1.20000000E+001 [angstrom]

  Usage: CUTOFF {real}

  Atomic Cutoff Radius Cutoff for the evaluation of the Exchange integrals. For non-periodic calculation the default value is exactly the full cell dimension, in order to evaluate all pair interactions. Instead, for periodic calculations the default is the minimum value between 1/4 of the cell dimension and the value specified in input (either explicitly defined or the default numerical value). [Edit on GitHub]

RC_RANGE: real = 0.00000000E+000 [angstrom]

  Usage: RC_RANGE {real}

  Range of cutoff switch function (tapering): 0.5*(1-TANH((r-r0)/RC_RANGE)), where r0=2.0RC_TAPER-20.0RC_RANGE. [Edit on GitHub]

RC_TAPER: real = [angstrom]

  Usage: RC_TAPER {real}

  Atomic Cutoff Radius Cutoff for Tapering Exchange integrals. If not specified it assumes the same value specified for the CUTOFF. [Edit on GitHub]