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Gaussian Basis

Jong Ho Choi

In short, a Gaussian basis set is a set of functions that is a linear combination of Gaussian functions. A basis set is a set of functions to describe molecular orbitals by expressing them as a linear combination of the atomic orbital analogies. Theoretically, the basis set can have any functional form, and a molecular orbital can be expanded to any function without approximation if the basis set is complete. As the number of atomic orbitals is infinite, the complete basis set should have also infinite number of functions.

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Geometry Optimization

Keerthi Mani

Geometry optimization is the process of adjusting the positions of atoms in a system to minimize its total energy. It is a crucial aspect in computational chemistry studies involving the structure and reactivity of molecules. Under the Born-Oppenheimer approximation which is separating the nuclear and electronic wavefunction, the geometry of a molecule at zero temperature is equivalent to the minimum of its potential energy surface.

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Ghost Atom

Nathan Lopez

A ghost atom is a point in space where a basis function is assigned but has no nuclear charge. Usually, basis functions are only placed at the center of nuclei, but if we place basis functions at arbitrary points in space, but do not place a nuclei there, then we have a ghost atom. We usually invoke ghost atoms when we are calculating…

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