Change in hybrid/coulombmatrix.F90 to obtain better agreement with ancient fleur
Recently an old subroutine to calculate spherical harmonics, harmonicsr, was replaced in the hybrid functionals code by the more commonly used ylm4 subroutine. It turns out that there is a case in which these subroutines yield differing results: The theta and phi angles in the routines are calculated from a vector that is passed to them. But at some places this vector has a length of 0.0. In ylm4 this leads to the assumption that the vector points in z direction. This leads to all m=0 Y_lm(theta,phi) having finite values. In the old subroutine a vanishing vector length lead to an averaging over all angles. For l=0, m=0 this is the same as in ylm4. But for all other l,m combinations the Y_lm(theta,phi) values vanish. In most cases these different behaviors are irrelevant. But there seem to be places where this leads to non-negligible differences in out-file values.
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