# How are 1-electron and 2-electron integrals done in PySCF?

I am right now using the PySCF for some quantum chemistry problems. I need to get the parameters, which are labeled $$h_{ij}$$ and $$V_{ijkl}$$. How can I get this done with PySCF?

• +1. Welcome to our new community, and we hope to see much more of you in the future!!! Thank you for contributing your question here, and joining us. The "parameters" to which you refer, are called "integrals", so I've changed the question so that more of our community will know what you're seeking. Feb 5 at 19:04

## 1 Answer

While this earlier question on our site was asking why fewer 2e- integrals were printed by PySCF than expected, and your question is simply asking how to calculate the 1e- and 2e- integrals in the first place (so the two questions are not duplicated), that question gave an excellent example for how to print the 2e- integrals for the He atom in a 6-31g basis set:

from pyscf import gto
mol = gto.M(atom='He 0 0 0', basis='6-31g')
eri = mol.intor('int2e', aosym='s8')
print(eri)


Similarly you can get the 1e- integrals by changing int2e to int1e.

• If he specifically wants $V_{ijkl}$ then aosym='s1' is likely a better option to include in your answer. Additionally, there is no such intor named int1e, so that will raise an Exception - if it is the 'core' Hamiltonian (nuclear + kinetic), then use mol.get_hcore(). That is equivalent to mol.intor('int1e_nuc') + mol.intor('int1e_kin'). Jul 11 at 11:20