Fix nuclear repulsion energy for single atom case.
Fix nuclear repulsion energy for single atom case.

gkc1000/pyscf,gkc1000/pyscf,sunqm/pyscf,sunqm/pyscf,sunqm/pyscf,gkc1000/pyscf,gkc1000/pyscf,sunqm/pyscf,gkc1000/pyscf