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License: MIT License
Simple code for quantum chemistry
License: MIT License
Effective Hamiltonian at the quantum chemistry level of theory is useful for modeling complex systems.
Löwdin charge analysis is described in Szabo (in English) p.152. Its implementation makes you fully understand the algorithm and code of Hartree-Fock theory.
Two approaches for the implementation are described below for the closed shell calculations (self._spin_multiplicity == 1). They can be implemented only by modifying hf_ksdft.py. Hereafter, AO and MO indicate atomic orbitals (or basis functions) and molecular orbitals. P is the density matrix in nonorthogonal AO basis (the dimension is (num_AO, num_AO) where num_AO is the number of atomic orbitals). S is the AO overlap matrix in nonorthogonal AO basis (the dimension is (num_AO, num_AO)). For the orthogonal and nonorthogonal AO basis, please check pp.142-145 in Szabo.
For the code development; (1) Make a new branch by, e.g., "git branch lowdin_charge" in master branch, (2) Do code development at the new branch, (3) Do git commit of the developed code, (4) Do git push, (5) Do pull request in the GitHub webpage.
Please check the result by comparing with the Gaussian's result with IOp(6/80=1) keyword for the Löwdin charge analysis. Note that because of the symmetry N2 has 0 charges. H2O has finite charges and could be a good test system.
Please also challenge the Löwdin charge analysis for the unrestricted calculations (self._spin_multiplicity != 1).
Implementation of numerical integration for the exchange-correlation potential and energy is required to complete KS-DFT. Psi4's VBase will be helpful for this problem. I am working on a branch "ksdft". The implementation of LDA exchange functional is a good starting point, I think.
Just a few modifications of the CIS code
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