-------------------------------------------------------------------- H2 @ R=0.5 bohr, aug-cc-pVTZ — n_basis = 46 -------------------------------------------------------------------- -------------------------------------------------------------------- Pre-flight linear-dependence check -------------------------------------------------------------------- Linear-dependence check [molecular AO overlap]: Basis is near-linearly-dependent (warning) ---------------------------------------------------- basis dimension: 46 min eigenvalue of S: 1.858e-07 max eigenvalue of S: 5.163e+00 condition number: 2.779e+07 eigenvalues below warn (1e-06): 1 eigenvalues below error (1e-08): 0 lowest 6 eigenvalues: 1.858e-07, 1.093e-04, 8.162e-04, 8.162e-04, 1.628e-03, 1.932e-03 Top 10 basis functions contributing to the near-null space: bf shell atom l a_min weight 2 2 0 0 0.1027 0.4960 25 11 1 0 0.1027 0.4960 16 7 0 1 0.1020 0.0032 39 16 1 1 0.1020 0.0032 24 10 1 0 0.3258 0.0008 1 1 0 0 0.3258 0.0008 37 15 1 0 0.0253 0.0000 14 6 0 0 0.0253 0.0000 30 13 1 1 0.3880 0.0000 7 4 0 1 0.3880 0.0000 Action: the SCF may still converge if you tighten damping or DIIS. A planned canonical-orthogonalisation path will make this case routine. -------------------------------------------------------------------- Default-path SCF (linear_dep_threshold = 1e-7) -------------------------------------------------------------------- run_job Job: RHF basis=aug-cc-pvtz ------------------------------------ Threads: 18 (OpenMP shared-memory parallelism) Output file: output-h2-tight-canonical-orth.out Starting molecular SCF (RHF). Per-iteration progress runs in compiled C++ and is not streamed live; the trace will be written when the SCF returns. SCF converged in 8 iterations; E = -0.4800444363 Ha [write_molden] - output-h2-tight-canonical-orth.molden [write_molden] done ( 1.2ms) [write_population] - output-h2-tight-canonical-orth.population.txt [write_population] done ( 1.0ms) [write_xyz] - output-h2-tight-canonical-orth.xyz [write_xyz] done ( 0.1ms) Job total 0.07s -- output written to output-h2-tight-canonical-orth.out converged = True iterations = 8 E(RHF) = -0.4800444363 Ha MO basis = (46, 46) [dropped 0 near-null directions] -------------------------------------------------------------------- Threshold sweep -------------------------------------------------------------------- threshold kept iters E (Ha) ΔE (µHa) 1e-09 46 8 -0.4800444363 +0.000 1e-07 46 8 -0.4800444363 +0.000 1e-05 45 8 -0.4800444363 +0.000 1e-03 42 8 -0.4800444363 +0.000 -------------------------------------------------------------------- Takeaway -------------------------------------------------------------------- Raising the threshold drops progressively more near-null directions; E stays stable to ~1 µHa across three decades of threshold choice. On well-conditioned bases the default 1e-7 never projects — the machinery only activates where it's genuinely needed.