-------------------------------------------------------------------- H2 @ R=0.5 bohr, aug-cc-pVTZ — n_basis = 46 -------------------------------------------------------------------- -------------------------------------------------------------------- Pre-flight linear-dependence check -------------------------------------------------------------------- Linear-dependence check: 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 α_min weight 2 2 0 0 0.1027 0.4960 25 11 1 0 0.1027 0.4960 39 16 1 1 0.1020 0.0032 16 7 0 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) -------------------------------------------------------------------- converged = True iterations = 7 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 7 -0.4800444363 +0.000 1e-07 46 7 -0.4800444363 +0.000 1e-05 45 7 -0.4800444363 +0.000 1e-03 42 7 -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.