# 2.9. HORTON dictionary of variables¶

For a full list of class names and variables, consult the Index.

## 2.9.1. Rules¶

The following naming rules are used in the HORTON source code:

- Lower and upper case is used according to PEP8. In share:
`CamelCase`

for class names,`lower_case`

for anything else. In lower-case names, underscore may be used to improve readability. For details, see: http://legacy.python.org/dev/peps/pep-0008/#prescriptive-naming-conventions. - Except for local variables inside one function or method, variable names should at least have two characters.
- Lists or arrays are often written in the plural form, e.g.
`coordinates`

. - When a variable represents a number of elements of some kind, the prefix
`n`

is used, e.g.`natom`

. - For integer loop variables, use the prefix
`i`

, e.g.`iatom`

. (Often a single`i`

and`j`

are still used for this purpose.)

## 2.9.2. Variable names and prefixes¶

- at
- Common prefix for a variable related to an atom. (Used when similar
variables exist that are not related to atoms, e.g.
`atgrid`

.) - coordintes
- 3D Cartesian coordinates of the nuclei. (Singular form is also used for the coordinate of a single atom.)
- dm
- A density matrix. (
`dm_full`

,`dm_spin`

,`dm_alpha`

,`dm_beta`

for spin-summed, spin difference, alpha and beta density matrices.) - er or electron_repulsion
- The electron repulsion two-body operator.
- fock
- A Fock matrix.
- exp
- An expansion of orbitals in a basis set, with orbital energies and
occupation numbers. (
`exp_alpha`

and`exp_beta`

are typically used for alpha and beta orbitals, respectively.) - grid
- The specification of an integration grid: the Cartesian coordinates of all the grid points and the corresponding integration weights.
- ham
- An (effective) hamiltonian.
- kin or kinetic
- The kinetic energy operator.
- lf
- A
`LinalgFactory`

instance. - mol
- A
`IOData`

instance. - moldens
- The spin-summed electron density (typically as an array of electron density values evaluated on a grid.)
- na or nuclear_attraction
- The nuclear attraction operator.
- numbers
- An array with atomic numbers. (Singular form is also used for the atomic number of a single atom.)
- log
- The screen logger of HORTON (See horton.log.)
- obasis
- An orbital basis.
- occ_model
- A model to assign occupation numbers to orbitals.
- olp or overlap
- The overlap operator.
- pseudo_numbers
- Effective core charges. (Singular form is also used for the effective core charge of a single atom.)
- scf_solver
- An algorithm to optimize the orbitals as to minimize the energy of an effective Hamiltonian.
- spindens
- The alpha - beta electron density (typically as an array of electron density values evaluated on a grid.)
- wpart or cpart
- A partitioning scheme.