Overlap of polarised basis elements not normalised

[Elious]

Hi NWChem community,

I was just checking the overlap matrix (overlap of basis functions) in NWChem-7.0.0. I used 6-31G* basis for Ethylene molecule. I found that all the individual basis elements are normalized (self-overlap is 1.00000) but the self-overlap polarised elements (dxy, dyz,dxz) gives 0.33333. Also when I manually calculated the self-overlap of dxy, dyx and dxz in cartesian basis, it comes out to be  0.26869 (with the coefficients and exponents taken from NWChem). Can you explain why the polarised basis functions are not normalized and how does this overlap in NWChem comes out to be 0.33333? 

Thanks

Md. Elious Ali Mondal

IISER Bhopal

[Edoardo Aprà]

Different normalization conventions are can be chosen for gaussian integrals..

The normalization convention used by NWChem is the same as the one described in

https://github.com/evaleev/libint/wiki/using-modern-CPlusPlus-API#normalization-and-layout-conventions

Some more details at

https://github.com/evaleev/libint/issues/20