# Uncertainties on atomic data. A case study: N IV

## TL;DR

This study compares three large-scale atomic data calculations for N IV, finding that despite discrepancies in collision strengths, spectral line intensities agree well, supporting their reliability for plasma diagnostics and quantifying uncertainties in rates.

## Contribution

It provides a comprehensive comparison of different computational methods for N IV atomic data and assesses their impact on plasma diagnostic ratios.

## Key findings

- Spectral line intensities agree within 20% despite differences in collision data.
- Uncertainties in atomic rates can significantly affect plasma diagnostic ratios.
- Monte Carlo analysis quantifies the impact of rate uncertainties on diagnostics.

## Abstract

We consider three recent large-scale calculations for the radiative and electron-impact excitation data of N IV, carried out with different methods and codes. The scattering calculations employed the relativistic Dirac $R$-matrix (DARC) method, the intermediate coupling frame transformation (ICFT) $R$-matrix method, and the B-spline $R$-matrix (BSR) method. These are all large-scale scattering calculations with well-tested and sophisticated codes, which use the same set of target states. One concern raised in previous literature is related to the increasingly large discrepancies in the effective collision strengths between the three sets of calculations for increasingly weak and/or high-lying transitions. We have built three model ions and calculated the intensities of all the main spectral lines in this ion. We have found that, despite such large differences, excellent agreement (to within $\pm$~20\%) exists between all the spectroscopically-relevant line intensities. This provides confidence in the reliability of the calculations for plasma diagnostics. We have used the differences in the radiative and excitation rates amongst the three sets of calculations to obtain a measure of the uncertainty in each rate. Using a Monte Carlo approach, we have shown how these uncertainties affect the main theoretical ratios which are used to measure electron densities and temperatures.