Reference: https://content.wolfram.com/sites/19/2012/02/Ho.pdf
I reproduced most of the computations in the MATHMATICA reference. The water molecule is a planar molecule that lies in the YZ-plane.
Source code for the solutions to Exercise 1.18 and 1.19.
I modified my translation of a FORTRAN program mentioned in a couple of my recent blog entries. The hybrid C/C++ source code is 1,291 lines. I find the basis set of Gaussian Type 1s Orbitals (GTO-NG) using my evolutionary hill-climber, where the GTO1s-NGs curve fit a Slater Type 1s Orbital (STO1s-NG), where N = 4 and 5 in the cation case and N = 4 in the molecule calculation. The percent errors in both cases are considerably less than 1%.
Using my STO-4G curve fit for N = 4 basis Gaussian type 1s orbitals I was able to get better results than found using the N = 3 basis wavefunctions in the graduate-level textbook Modern Quantum Chemistry Introduction to Advanced Electronic Structure Theory by Attila Szabo and Neil S. Ostlund. My recreation for N = 3 discovered -2.97867 atomic units ground state energy for the helium-hydrogen ion and -1.11651 atomic units for the hydrogen molecule using the textbook’s basis wavefunctions. The percentage errors were 3.98002% and 4.15928% respectively. My STO-4G basis wavefunctions found a ground state energy for the helium-hydrogen ion of -2.94937 atomic units and for the hydrogen molecule -1.14344 atomic units, which have percentage errors of 0.98349% and 2.86607% respectively.
On Wednesday, October 16, 2024, I bought an Amazon Kindle book named “Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory” by Attila Szabo and Neil S. Ostlund. It cost me $10.69 which is a real bargain. In Appendix B there is a listing for a FORTRAN program to perform an ab initio Hartree-Fock Self Consistent Field calculation for a two-electron heteronuclear molecule namely the helium-hydrogen cation. I successfully translated the program from FORTRAN to C++. I had to remember that FORTRAN stores matrices in column major order and C/C++ stores matrices in row major order. I took the transposes of two FORTRAN COMMON matrices to get the correct C++ storage. The authors of the book did an extensive treatment of the test calculation. The application is only 823 lines of monolithic C++ source code. I used FORTRAN like array indexing starting at 1 instead of the C initial beginning index of 0. I think I will try to get in touch with the authors to get permission to post the source code and results on my blog.
P. S. I got permission from Dover Books to publish my source code and results. I think I will reconsider posting the C++ source code. The actual ground state energy of the cation is -2.97867. My calculation and the book’s computation are in percentage errors of about 4%. The book’s value is a little closer to the exact value than my result. The book calculation was done in FORTRAN double precision on a Digital Equipment Corporation PDP-10 minicomputer. My recreation of the book’s endeavor was executed on an Intel Itanium Core 7 and Windows 10 Professional machine using Win32 C++. The C++ compiler was from Microsoft Visual Studio 2019 Community Version.
Note I added a calculation for a homonuclear molecule, namely, the hydrogen diatomic molecule.
References: https://web.stanford.edu/~oas/SI/QM/Atkins05.pdf See Example 8.1 The evaluation of overlap and Coulomb integral for the hydrogen molecule ion pages 255 – 256 https://www.physics.udel.edu/~jim/PHYS425_20S/Class%20Notes/Notes_8.pdf https://phys.libretexts.org/Bookshelves/Quantum_Mechanics/Introductory_Quantum_Mechanics_(Fitzpatrick)/13%3A_Variational_Methods/13.03%3A_Hydrogen_Molecule_Ion#fh2pa
Numerical Explorations 