# XAS

References: Iannuzzi2007

Sets the method of choice to calculate core-level excitation spectra. The occupied states from which we calculate the excitation should be specified. Localization of the orbitals may be useful. [Edit on GitHub]

Subsections

- LOCALIZE
- PRINT
- SCF

## Keywords

- SECTION_PARAMETERS

- ADDED_MOS

- ATOMS_LIST

- DIPOLE_FORM

- EPS_ADDED

- MAX_ITER_ADDED

- METHOD

- NGAUSS

- ORBITAL_LIST

- OVERLAP_THRESHOLD

- RESTART

- SPIN_CHANNEL

- STATE_SEARCH

- STATE_TYPE

- WFN_RESTART_FILE_NAME

- XAS_CORE

- XAS_TOT_EL

- XES_CORE

- XES_EMPTY_HOMO

## Keyword descriptions

SECTION_PARAMETERS: logical = F

  Lone keyword: `T`

  Usage: &XAS T

  controls the activation of core-level spectroscopy simulations [Edit on GitHub]

ADDED_MOS: integer = -1

  Usage: ADDED_MOS {integer}

  Number of additional MOS added spin up only [Edit on GitHub]

ATOMS_LIST: integer[ ]

  Keyword can be repeated.

  Aliases: AT_LIST

  Usage: ATOMS_LIST {integer} {integer} .. {integer}

  Indexes of the atoms to be excited. This keyword can be repeated several times (useful if you have to specify many indexes). [Edit on GitHub]

DIPOLE_FORM: enum = VELOCITY

  Aliases: DIP_FORM

  Usage: DIPOLE_FORM string

  Valid values:

  - `LENGTH` Length form ⟨ i | e r | j ⟩

  - `VELOCITY` Velocity form ⟨ i | d/dr | j ⟩

  Type of integral to get the oscillator strengths in the diipole approximation [Edit on GitHub]

EPS_ADDED: real = 1.00000000E-005

  Usage: EPS_ADDED 1.e-6

  target accuracy incalculation of the added orbitals [Edit on GitHub]

MAX_ITER_ADDED: integer = 2999

  Usage: MAX_ITER_ADDED 100

  maximum number of iteration in calculation of added orbitals [Edit on GitHub]

METHOD: enum = NONE

  Aliases: XAS_METHOD

  Usage: METHOD TP_HH

  Valid values:

  - `NONE` No core electron spectroscopy

  - `TP_HH` Transition potential half-hole

  - `TP_FH` Transition potential full-hole

  - `TP_VAL` Hole in homo for X-ray emission only

  - `TP_XHH` Transition potential excited half-hole

  - `TP_XFH` Transition potential excited full-hole

  - `DSCF` DSCF calculations to compute the first (core)excited state

  - `TP_FLEX` Transition potential with generalized core occupation and total number of electrons

  Method to be used to calculate core-level excitation spectra [Edit on GitHub]

NGAUSS: integer = 3

  Usage: NGAUSS {integer}

  Number of gto’s for the expansion of the STO of the type given by STATE_TYPE [Edit on GitHub]

ORBITAL_LIST: integer[ ]

  Keyword can be repeated.

  Aliases: ORBITAL_LIST

  Usage: ORBITAL_LIST {integer} {integer} .. {integer}

  Indices of the localized orbitals to be excited. This keyword can be repeated several times (useful if you have to specify many indexes). [Edit on GitHub]

OVERLAP_THRESHOLD: real = 1.00000000E+000

  Usage: OVERLAP_THRESHOLD 8.e-1

  Threshold for including more than one initial core excited state per atom. The threshold is taken relative to the maximum overlap. [Edit on GitHub]

RESTART: logical = F

  Lone keyword: `T`

  Usage: RESTART

  Restart the excited state if the restart file exists [Edit on GitHub]

SPIN_CHANNEL: integer = 1

  Usage: SPIN_CHANNEL 1

  # Spin channel of the excited orbital [Edit on GitHub]

STATE_SEARCH: integer = -1

  Usage: STATE_SEARCH 1

  # of states where to look for the one to be excited [Edit on GitHub]

STATE_TYPE: enum = 1S

  Aliases: TYPE

  Usage: STATE_TYPE 1S

  Valid values:

  - `1S` 1s orbitals

  - `2S` 2s orbitals

  - `2P` 2p orbitals

  - `3S` 3s orbitals

  - `3P` 3p orbitals

  - `3D` 3d orbitals

  - `4S` 4s orbitals

  - `4P` 4p orbitals

  - `4D` 4d orbitals

  - `4F` 4f orbitals

  Type of the orbitals that are excited for the xas spectra calculation [Edit on GitHub]

WFN_RESTART_FILE_NAME: string

  Aliases: RESTART_FILE_NAME

  Usage: WFN_RESTART_FILE_NAME <FILENAME>

  Root of the file names where to read the MOS from which to restart the calculation of the core level excited states [Edit on GitHub]

XAS_CORE: real = 5.00000000E-001

  Usage: XAS_CORE 0.5

  Occupation of the core state in XAS calculation by TP_FLEX. [Edit on GitHub]

XAS_TOT_EL: real = -1.00000000E+000

  Usage: XAS_TOT_EL 10

  Total number of electrons for spin channel alpha, in XAS calculation by TP_FLEX. If it is a negative value, the number of electrons is set to GS number of electrons minus the amount subtracted from the core state [Edit on GitHub]

XES_CORE: real = 1.00000000E+000

  Usage: XES_CORE 0.5

  Occupation of the core state in XES calculation by TP_VAL. The HOMO is emptied by the same amount. [Edit on GitHub]

XES_EMPTY_HOMO: logical = F

  Lone keyword: `T`

  Usage: XES_EMPTY_HOMO

  Set the occupation of the HOMO in XES calculation by TP_VAL. The HOMO can be emptied or not, if the core is still full. [Edit on GitHub]