The 4-index 2-electron integral can be obtained for the He atom with the following code:
import numpy as np from pyscf import gto, scf, ao2mo mol = gto.Mole() mol.atom = """ He 0. 0. 0. """ mol.basis = "cc-pvdz" mol.build() # Run Hartree-Fock. mf = scf.RHF(mol) mf.kernel() # Find electron-repulsion integrals (eri). eri = ao2mo.kernel(mol, mf.mo_coeff) eri = np.asarray(ao2mo.restore(1, eri, mol.nao))
I am interested in obtaining the 2-index (A) and 3-index (CIAB) matrices, which can be used to form the 4-index 2-electron (eri) integral. I have looked at the list of possible means by which this is accomplished in PySCF code; however, I am unsure of the correct answer.