Fix value conversion warnings in SlaterSet
Fix value conversion warnings in SlaterSet

This fixes a number of value conversion warnings for methods
in the SlaterSet class.

Change-Id: Iefc93baacbfecdd18eccd717b38d465f16c1d9ff

OpenChemistry/openqube,OpenChemistry/openqube,OpenChemistry/openqube,OpenChemistry/openqube