Dear CP2K Developers, I am writing to ask for your advice regarding some small but systematic discrepancies I observed in density matrices and Mulliken population analysis obtained from a single‐point calculation performed using CP2K. In my test for CO, I compared the following files generated from the same single-point SCF calculation: <ol> <li> The MOLDEN file (CO_molopt_smearing-mos.molden-1_0.molden) </li> <li> The Mulliken file (CO_molopt_smearing-mulliken-1.mulliken) </li> <li> The largest iteration AO log file (e.g., CO_molopt_smearing-ao-1_0_12.Log) </li> <li> The 1_0 AO log file (CO_molopt_smearing-ao-1_0.Log) </li> </ol> I found that: <ul> <li> The density matrices read from the last AO log file and from the 1_0 AO file differ by approximately 1×10⁻⁷, even though they originate from the same single-point calculation. </li> <li> Constructing Mulliken populations by element-wise multiplication of the density matrix P and the overlap matrix S (i.e., computing PμνSμν for each pair of atomic orbitals) leads to slightly different values compared to the MULLIKEN NET ATOMIC ORBITAL AND OVERLAP POPULATION MATRIX reported in CP2K’s Mulliken output file. </li> <li> Additionally, when processing the MOLDEN file using Multiwfn, the computed Mulliken bond orders are again slightly different from those obtained directly from CP2K. </li> </ul> Before I proceed further, I would like to confirm: <ol> <li> Are these ~1e−7 differences expected due to formatting, truncation, numerical precision, or different internal representations used when writing the log files, MOLDEN file, and Mulliken file? </li> <li> Is there a recommended “most reliable” source of the density matrix for reproducing CP2K Mulliken results (Mulliken file vs. AO log file vs. MOLDEN file)? </li> <li> Are the Mulliken matrices produced by CP2K post‐processed in any additional way (e.g., symmetrization, thresholding) that could explain these differences? </li> <li> Are there known limitations or differences in the basis function ordering between MOLDEN export and the AO log files? </li> </ol> For reference, I attach (or can provide) the following files: <div><div><div><div></div></div></div><div dir="ltr">CO_molopt_smearing.inp CO_molopt_smearing.out CO_molopt_smearing-mulliken-1.mulliken CO_molopt_smearing-mos.molden-1_0.molden CO_molopt_smearing-ao-1_0.Log CO_molopt_smearing-ao-1_0_12.Log </div></div> Any guidance on how to interpret these discrepancies would be greatly kind of you. Thank you very much for your time and for your continuous development of CP2K. Best regards -- You received this message because you are subscribed to the Google Groups "cp2k" group. To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsubscribe@googlegroups.com">cp2k+unsubscribe@googlegroups.com</a>. To view this discussion visit <a href="https://groups.google.com/d/msgid/cp2k/b263b616-bf70-463b-a9e5-7ad8561fa1e7n%40googlegroups.com?utm_medium=email&utm_source=footer">https://groups.google.com/d/msgid/cp2k/b263b616-bf70-463b-a9e5-7ad8561fa1e7n%40googlegroups.com</a>.