Does PySCF use chemist's or physicist's notation for 1- and 2-electron integrals?

Question

I am trying to evaluate 1- and 2-electron integrals using PySCF trough this code:

Hij = mol.intor('int1e_kin') + mol.intor('int1e_nuc')
Vijkl = mol.intor('int2e') 

where I previously defined mol in a particular basis.

I am new in this software and I am reading the basic tutorials that offers the project's site here, but so far I can't find if the elements Vijkl of the 2-electron integrals are define in the chemist's notation, $$ V_{ijkl} = (ij|kl) = \int \frac{\phi^*_i(\mathbf{r}_1)\phi_j(\mathbf{r}_1)\,\phi^*_k(\mathbf{r}_2)\phi_l(\mathbf{r}_2)}{|\mathbf{r}_1 - \mathbf{r}_2|}\,d\mathbf{r}_1d\mathbf{r}_2, $$ or physicist's notation, which is $$ V_{ijkl} = \langle ij|kl \rangle = \int \frac{\phi^*_i(\mathbf{r}_1)\phi_j^*(\mathbf{r}_2)\,\phi_k(\mathbf{r}_1)\phi_l(\mathbf{r}_2)}{|\mathbf{r}_1 - \mathbf{r}_2|}\,d\mathbf{r}_1d\mathbf{r}_2. $$

I am assuming that the program uses chemist's notation. Am I right? And, if so, is it a way to easily convert the array into the other convention? Thank you all in advanced.

Answer 1

You are right that pyscf uses chemist's notation. A quick google search with the keywords pyscf chemist notation and electron integrals returned these two hits for FCI and CC. Reading through the documentation, it is mentioned that the integrals are treated in chemist's notation.

To address the point that Prof. Dattani made, if you instead search for physicist's notation, you will find that as an argument for this function pyscf.cc.gintermediates.get_t3p2_imds_slow in the page for CC. I also found the mention of physicist's notation in this page.