-------------------------------------------------------------------- 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). iter 1 E = -0.4758381154 Ha ||[F,DS]|| = 3.213e-01 DIIS= 1 attempt=1 [ 190.3ms] iter 2 E = -0.4798360777 Ha dE = -3.998e-03 ||[F,DS]|| = 6.639e-02 DIIS= 2 attempt=1 [ 194.2ms] iter 3 E = -0.4800441617 Ha dE = -2.081e-04 ||[F,DS]|| = 2.123e-03 DIIS= 3 attempt=1 [ 197.4ms] iter 4 E = -0.4800444360 Ha dE = -2.743e-07 ||[F,DS]|| = 5.744e-05 DIIS= 4 attempt=1 [ 200.9ms] iter 5 E = -0.4800444363 Ha dE = -3.610e-10 ||[F,DS]|| = 5.189e-06 DIIS= 5 attempt=1 [ 206.3ms] iter 6 E = -0.4800444363 Ha dE = -2.206e-12 ||[F,DS]|| = 4.984e-07 DIIS= 6 attempt=1 [ 210.3ms] SCF converged in 6 iterations; E = -0.4800444363 Ha [write_population] - output-h2-tight-canonical-orth.population.txt [write_population] done ( 63.9ms) [write_xyz] - output-h2-tight-canonical-orth.xyz [write_xyz] done ( 2.0ms) [write_molden] - output-h2-tight-canonical-orth.molden [write_molden] done ( 8.5ms) Job total 0.34s -- output written to output-h2-tight-canonical-orth.out converged = True iterations = 6 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 6 -0.4800444363 +0.000 1e-07 46 6 -0.4800444363 +0.000 1e-05 45 6 -0.4800444363 +0.000 1e-03 42 6 -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.