aromanro/hartreefock

A program implementing the Hartree–Fock (also post-HF: MP2, CCSD(T), CIS and TDHF/RPA)/self-consistent field method (also DIIS) with Gaussian orbitals

hartreefock's Issues

Add GW?

Another one possible: https://en.wikipedia.org/wiki/GW_approximation
There are plenty of articles on this (for example: https://aip.scitation.org/doi/10.1063/1.4718428) and a good book, "Interacting Electrons: Theory and Computational Approaches" by Richard Martin et al.

Add electric field term to the Hamiltonian

Only the 'core' part needs to be changed, it's not so hard.

The advantage would be to be able to calculate the electric dipole moment using the derivative of energy with respect to the electric field.

For details, see 6.101 and the explanation before it from Szabo & Ostlund, Modern Quantum Chemistry. Introduction to Advanced Electronic Structure Theory.

Structural computations

Having this #16 implemented, it's just an optimization problem.

The code could compute the molecule structure.

3D charting of orbitals

A surface or volumetric visualization with VTK

Add population analysis

As in the last paragraph here: https://github.com/CrawfordGroup/ProgrammingProjects/tree/master/Project%2303

Add more basis sets

In principle the program should be able to use a different number of Gaussians in the inner shell than in the valence shell, so it could work with orbital sets like 3-21G or 6-21G. Maybe the parsing code should be changed for that, but it should be possible to use them.

Add option to chart Hartrees instead of eV

The energy is usually given in Hartrees in the literature, so this would help checking the results

Implement CC for the unrestricted method

Currently I'm implementing https://en.wikipedia.org/wiki/Coupled_cluster for the restricted method, hopefully that will succeed, but probably I'll postpone indefinitely the implementation for the unrestricted method.

I'll leave the issue opened for the future...

Add computation of dipole-moment integrals

Would be nice to be able to compute more, like polarizability or transition dipole moment.
Probably won't happen soon.

Results are wrong if orbitals with L>1 are involved

First I noticed the wrong results by testing some * basis sets, but it turned out that the results are wrong even for STOnG if a D orbital is involved. As results come lower than the Hartree Fock limit, this is very probably a bug in integrals computation.

Vibrational spectra

Having this #16 implemented, vibrational modes and frequencies could be computed.

It could even go further, computing line intensities.

Add dynamic dipole polarizability and photoabsorption spectrum computation

Together with some other things (not only time dependent but also time independent), they are for example briefly described in
'Introduction to the calculation of molecular properties by response theory' by Joulien Toulouse.

Add possibility to specify occupation of orbitals

This would allow for example to compute excited states.

Implement Davidson-Liu algorithms for CIS

As described in this tutorial: https://github.com/CrawfordGroup/ProgrammingProjects/tree/master/Project%2313

Implement CIS and TDHF/RPA for unrestricted method?

I'll see if I'll do it...

Add DIIS

https://en.wikipedia.org/wiki/DIIS

Add post Hartree-Fock method(s) to improve results

For example:
https://en.wikipedia.org/wiki/M%C3%B8ller%E2%80%93Plesset_perturbation_theory
https://en.wikipedia.org/wiki/Coupled_cluster
https://en.wikipedia.org/wiki/Configuration_interaction

Add DFT

Another thing that probably won't happen soon - but it's something that is possible - is to add DFT to the project.

Compute gradient, Hessian matrix

The derivatives could be computed numerically (central difference would be my choice).
In fact, they could be computed 'analytically', but I don't think I would use that method for this project, I suppose the post-HF things would complicate things even more.

They could be used for optimizations computations, that is, computation of molecular structure.
Also vibrational modes & frequencies could be computed.
Ideally, also the lines intensity...

Add * orbitals

Add unoccupied/polarization orbitals to the basis set (as in STO-3G* or 3-21G*).

Add Car-Parrinello?

Similar, but more complex, with what it's already implemented in python: https://github.com/aromanro/PythonCompphys/blob/master/Car-Parrinello.ipynb

The complexity stems from those derivatives, that's what stopped me to implement it first here. It's way simpler when using only 's orbitals'.

Implement CISD or CID

For now CIS for restricted method is implemented, to be used in TDHF/RPA.

Maybe I'll also implement at least CID.