# MOM

References: Gilbert2008, Barca2018

Define type and parameters for the maximum overlap method (MOM) to determine orbital occupancies. The MOM procedures activated by this section are only active for diagonalization methods, i.e. not with minimization methods based on OT. Incompatible with core-level excitation spectra (XAS). [Edit on GitHub]

## Keywords

- SECTION_PARAMETERS

- DEOCC_ALPHA

- DEOCC_BETA

- MOM_TYPE

- OCC_ALPHA

- OCC_BETA

- PROJ_FORMULA

- START_ITER

## Keyword descriptions

SECTION_PARAMETERS: logical = F

  Lone keyword: `T`

  Usage: MOM ON

  Controls the activation of the MOM procedure [Edit on GitHub]

DEOCC_ALPHA: integer[ ] = 0

  Usage: DEOCC_ALPHA 10 11 …

  Alpha orbitals to be deoccupied [Edit on GitHub]

DEOCC_BETA: integer[ ] = 0

  Usage: DEOCC_BETA 10 11 …

  Beta orbitals to be deoccupied [Edit on GitHub]

MOM_TYPE: enum = MOM

  Usage: MOM_TYPE mom

  Valid values:

  - `MOM` Originally proposed MOM protocol which uses molecular orbitals from the previous SCF cycle as reference

  - `IMOM` Initial-MOM which uses molecular orbitals of the initial guess as reference

  Revision of the maximum overlap method to be used [Edit on GitHub]

OCC_ALPHA: integer[ ] = 0

  Usage: OCC_ALPHA 12 15 …

  Alpha orbitals to be occupied [Edit on GitHub]

OCC_BETA: integer[ ] = 0

  Usage: OCC_BETA 12 15 …

  Beta orbitals to be occupied [Edit on GitHub]

PROJ_FORMULA: enum = NORM

  Usage: PROJ_FORMULA norm

  Valid values:

  - `NORM` The one which ignores the phase of molecular orbitals: proj_j = \sqrt(\sum_i overlap(i, j)^2)

  - `SUM` The one proposed in the original paper: proj_j = |\sum_i overlap(i, j)|

  Projection formula to be used [Edit on GitHub]

START_ITER: integer = 0

  Usage: START_ITER 2

  SCF iteration cycle to start the MOM procedure. Could be used for ground state calculations only in order to stabilise oscillating SCF iterations [Edit on GitHub]