$$\renewcommand{\AA}{\text{Å}}$$

# 11.2. Error and warning details¶

Many errors or warnings are self-explanatory and thus straightforward to resolve. However, there are also cases, where there is no single cause and explanation, where LAMMPS can only detect symptoms of an error but not the exact cause, or where the explanation needs to be more detailed than what can be fit into a message printed by the program. The following are discussions of such cases.

## 11.2.1. Unknown identifier in data file¶

This error happens when LAMMPS encounters a line of text in an unexpected format while reading a data file. This is most commonly cause by inconsistent header and section data. The header section informs LAMMPS how many entries or lines are expected in the various sections (like Atoms, Masses, Pair Coeffs, etc.) of the data file. If there is a mismatch, LAMMPS will either keep reading beyond the end of a section or stop reading before the section has ended.

Such a mismatch can happen unexpectedly when the first line of the data is not a comment as required by the format. That would result in LAMMPS expecting, for instance, 0 atoms because the “atoms” header line is treated as a comment.