# ARTS built-in documentation server

## Workspace Method abs_lines_per_speciesPopulationNlteField

### Description

Turns on NTLE calculations.
Takes the quantum identifers for NLTE temperatures and matches it to
lines in abs_lines_per_species. abs_species must be set and is used
to speed up calculations. After the function is done, all affected
lines in abs_lines_per_species will have an internal tag to the relevant
quantum identifier, which is a requirement for deeper code.
If vibrational_energies is input it must match nlte_level_identifiers
in length. The vibrational energies of the affected lines will then be
set by the function. Otherwise, it is assumed the vibrational energies
are set by another method. If they are not set, calculations will complain
later on while running deeper code.
For now only vibrational energy states are assumed to be able to be in
non-LTE conditions. The QuantumIdentifier for an energy state in ARTS
can look like:
"CO2-626 EN v1 0/1 v2 1/1 l2 1/1 v3 0/1 r 1/1"
and the matching will match ALL lines with the above. Note then that if, e.g.,
the "v1 0/1" term was removed from the above, then ARTS will assume that
"v1" is not part of the level of energy state of interest, so lines
of different "v1" will be matched as the same state. If a line is matched
to more than one energy state, errors should be thrown, but be careful.
Set type of population to change computations and expected input as:
LTE: Compute population by ratios found from LTE temperatures
TV: Compute population by ratios found from NLTE vibrational temperatures
ND: Compute population by ratios found from NLTE number densities

**Authors: **Richard Larsson

### Synopsis

### Variables