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Report SCF (HF/DFT) Convergence Issues
Questions

Dear Q-Chem Community, If you have any SCF (HF/DFT) jobs that are time-consuming or are facing convergence difficulties with Q-Chem, please send them to support@q-chem.com with the subject line “SCF Convergence Issue” t…

3 1038 November 22, 2024
Cannot get rid of Imaginary Frequency
Questions
1 20 November 24, 2025
TDA with RSH giving negative triplet excitation
Questions
11 109 November 24, 2025
“ADC(3) singlet and triplet excited states with PCM – input and disk quota issues”
Questions
3 311 November 21, 2025
vdW-TS (MBDVDW) vibrational frequencies
Questions
13 25 November 21, 2025
Second Derivative for DC-DFT
How To
9 197 November 21, 2025
TD-DFT geometry optimization using IEFPCM solvation model
Questions
1 40 November 20, 2025
Webinar 83: Coupled Cluster Developments in Q-Chem
Webinars
0 33 November 20, 2025
Obtaining cube file for mo's, suggesting bond breaking
Questions
2 39 November 19, 2025
Trouble using EOM-CCSD, with frozen core
Questions
6 69 November 19, 2025
Issue with S₁ State Optimization Under PCM – SCF Convergence Error
Questions
3 54 November 18, 2025
How to set broken‑symmetry state?
Questions
7 92 November 17, 2025
Problem oxygen potential energy scan using CCSD(T) and EA state PES using EA-EOM-CCSD
Questions
11 443 November 11, 2025
“double free or corruption (out)” error in TDDFT + EFP job with large number of fragments
Questions
1 92 November 9, 2025
Cannot escape an imaginary frequency
Questions
1 126 November 7, 2025
Limited support for analytic Hessians in Q-Chem
Questions
10 835 November 6, 2025
How does IQmol calculate the center of mass of a molecule?
Questions
1 123 November 1, 2025
TSVDW and MBD crashes
Questions
1 124 October 30, 2025
Unexpected behaviour: core orbitals are not frozen during MP2/MP3 step in ADC calculations
Questions
4 248 October 27, 2025
SCF convergence issue with diffuse functions on basis set
Questions
27 448 October 22, 2025
Crash upon frequency calculations with range separated bybrid
Questions
1 210 October 21, 2025
Cryptic import_xcfunc warning
Questions
10 327 October 20, 2025
What sort of RI techniques are safe to use with different types of SCF?
Questions
3 243 October 16, 2025
RI worsens SCF timings
Questions
4 260 October 16, 2025
EOMCCSDT calculations
How To
2 312 September 29, 2025
Question on calculating IPs (cationic states) for L-shell orbitals with IP-EOM-CCSD or ADC(3)
Questions
14 309 October 9, 2025
Is CVS approximation available for IP-ADC(3)?
Questions
0 214 October 9, 2025
Single Point immediately fails with DM alg and AUTOSAD guess
Questions
4 258 October 8, 2025
Keywords for printing <S^2> values using unrestricted TDDFT (RPA=2)
Questions
2 413 October 7, 2025
Clarification on RASSCF Calculation of Multiple Spin States in Q-Chem
Questions
2 272 October 6, 2025