**Glossary of terms used in theoretical
organic chemistry **

[A] [B]
[C] [D] [E]
[F] [G] [H]
[I] [J-K] [L]
[M]

[N] [O] [P]
[Q-R] [S] [T]
[U-V] [W-Z]

# **G**

**Gaussian type orbital** **(GTO**)
- An exponential function centered on an atom, the general expression
for which is given by

c (a, **r**)
= *Nx*^{i}y^{j}z^{k}exp(-a*r*^{2})

where *i*,* j*, *k* are positive integers or zero
and a is the orbital exponent. Orbitals of
s, p, and d type result when *i* + *j* + *k* = 0,
1, 2 respectively. Linear combinations of primitive gaussians are used
to form the actual *basis functions*
that are called contracted gaussians.The great convenience of GTOs
lies in the fact that evaluation of the molecular integrals needed in
*ab * *initio
quantum mechanical methods* of calculation is performed much
more efficiently as compared with *Slater
type atomic orbitals*.

**Generalized Valence Bond (GVB)
method** - A multiconfigurational method that uses a limited set
of valence bond configurations in the conventional *multiconfiguration
SCF method*.

**Ghost orbitals** - see *Counterpoise
correction*.

**Gradient norm** - see *Energy
gradient.*

**Graph **- A representation consisting of points
(vertices) connected by lines (edges). A graph is a topological,
but not a geometric object.

**Graph automorphism group **-
The set of all permutations of* graph *vertices
in which adjacent vertices remain adjacent.

**Ground state **-** **The lowest
energy state of a chemical entity.