The interaction of solids with gases is in itself a very rich subject which finds many scientific and technological applications. The...

When it comes to the properties of crystals, there are two central models in statistical mechanics. One is the the Einstein crystal,...

With the electronic contribution to the total energy available we can aim at describing nuclear motion and accounting for it in the...

But in order to go from the properties of one molecule to the properties of a large ensemble of them, we require a specific set of...

The Neglect of Diatomic Differential Overlap is the next level of approximations used in semiempirical quantum chemistry and the basis of...

The next extension in semiempirical MO theory come with the introduction of the intermediate neglect of differential overlap (INDO)...

The next advent in semiempirical methods comes with the introduction of the zero differential overlap approximation, which states that...

Perhaps the first semiempirical method worth exploring is the extended Hueckel, the generalisation of the Hueckel method for systems as...

Hartree-Fock (HF) theory belongs to a class of methods coined ab initio, because all molecular integrals that are required are...

As the PDF on HF showed, one also requires kinetic energy integrals and nuclear repulsion integrals. Unfortunately, I was not yet able to...

The first type of integrals required in quantum chemical calculations are overlap integrals. These measure the overlap between atomic...

In order to perform molecular calculations, one requires using a set of (precomputed) orbitals describing the atoms. Once again, the...

Much like poly electronic atoms, there is no analytical solution to the molecular Schroedinger equation. To get a (very) good...

Only with the advent of quantum mechanics it was possible to delve into the microscopic world of molecules and particles. Without the...

The next advent in semiempirical methods comes with the introduction of the zero differential overlap approximation, which states that...

When dealing with molecular physics, it is best to start by giving a solid basis on its foundation. And the foundations of molecules are...

The calculation of the overlap functions is usually done in a local frame where we place both atoms in one of the axis of the referential...