This keyword imposes time reversal symmetry on the gamma point wavefunctions. Time reversal symmetry is a necessary property of any Kohn-Sham orbital. NLXC_EXCHANGE_REFLECT_KPTS is the latest form of this keyword, while the obsolete version, EXCHANGE_REFLECT_KPTS, is supported for backward compatibility.
In the reciprocal space representation, time reversal symmetry means that the coefficient of plane wave |k + g> must be the conjugate of the coefficient of plane wave |-k - g>. With the standard LDA and GGA exchange-correlation functionals, the absence of such symmetry does not affect the total energies or densities and can therefore be ignored. However, when using exact or screened exchange, the total energy may be incorrect if time reversal symmetry is not present. Also, the efficiency of calculation of the exchange operator is significantly improved by assuming time reversal symmetry (see also NLXC_EXCHANGE_REFLECT_KPTS.
NLXC_IMPOSE_TRS : TRUE
CASTEP keyword glossary
CASTEP parameters keywords