NLSPLINE = .TRUE. | .FALSE.
Default: NLSPLINE = .FALSE.
Description: construct the PAW projectors in reciprocal space using spline interpolation so that they are k-differentiable.
For NLSPLINE=.TRUE., the PAW projectors in reciprocal space (LREAL=.FALSE.) are set up using a spline interpolation so that they are k-differentiable. This improves the susceptibility contribution to the chemical shifts. It only slightly affects the other contributions to the chemical shifts.
It is advised to set NLSPLINE=.TRUE. if and only if PAW projectors are applied in reciprocal space and chemical shifts are are calculated, i.e. if and only if LREAL=.FALSE. and LCHIMAG=.TRUE. As this option also gives slightly different total energies, it is advised to use the default NLSPLINE=.FALSE. in all other calculations for reasons of compatibility.
Real space projectors are k-differentiable by construction, hence do not require to set NLSPLINE=.TRUE.