The EXCHANGE and CORRELATION $rem variables (Chapter 4) allow the user to indicate that the exchange-correlation density functional will be user-defined. The user defined exchange-correlation is to be entered in the $xc_functional part of the input. The format is:
$xc_functional X exchange_symbol coefficient X exchange_symbol coefficient ... C correlation_symbol coefficient C correlation_symbol coefficient ... K coefficient $end
Note: Coefficients are real numbers.