Molecular Quantum Mechanics

Much like poly electronic atoms, there is no analytical solution to the molecular Schroedinger equation. To get a (very) good approximation to the molecular wavefunction, one uses the very powerful approximation of linear combination of atomic orbitals. This means that molecular orbitals, the wavefunctions describing electrons in molecules, are built by combining atomic orbitals. There are two main schools of thought in quantum chemistry, one is based on the Hartree-Fock (HF) method while the other is based on density functional theory (DFT). Even though there are recently great advances in Hartree-Fock based methods, there is an obvious dominance of DFT in the world of computational chemistry. This is because considerably good results can be obtained at an amenable computational cost, even though significantly more accurate results can be potentially obtained using post-HF methods. This is because DFT includes “to some extent” electron correlation effects.

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