Gaussian Examples

All examples locate the triplet/singlet (S=3 / S=1) MECP of the phenylcation (C₆H₅⁺, charge = 1). See Overview for the geometry and how to run.

Example 1 — Default GDIIS

The simplest production-ready input. Uses the default GDIIS optimizer with 3 warm-up BFGS steps.

nprocs = 10
mem = 40GB
method = n b3lyp/6-31g**
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = gaussian

*geom
C     0.000000000000      1.396613000000      0.000000000000
C     1.209503000000      0.698307000000      0.000000000000
C     1.209503000000     -0.698307000000      0.000000000000
C     0.000000000000     -1.396613000000      0.000000000000
C    -1.209503000000     -0.698307000000      0.000000000000
C    -1.209503000000      0.698307000000      0.000000000000
H     2.150882000000      1.241812000000      0.000000000000
H     2.150882000000     -1.241812000000      0.000000000000
H     0.000000000000     -2.483625000000      0.000000000000
H    -2.150882000000     -1.241812000000      0.000000000000
H    -2.150882000000      1.241812000000      0.000000000000
*

*tail_a
*

*tail_b
*

Key settings: switch_step = 3 (default), hessian = direct_psb (default), use_gediis = false (default).

Example 2 — Sequential Hybrid (GEDIIS → GDIIS)

Activates the 3-phase switching strategy of Li & Frisch (JCTC 2006). Adds only two lines to Example 1 and typically converges ~2–4× faster.

nprocs = 10
mem = 40GB
method = n b3lyp/6-31g**
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = gaussian

# --- optimizer ---
use_gediis = true
use_hybrid_gediis = true

*geom
C     0.000000000000      1.396613000000      0.000000000000
C     1.209503000000      0.698307000000      0.000000000000
C     1.209503000000     -0.698307000000      0.000000000000
C     0.000000000000     -1.396613000000      0.000000000000
C    -1.209503000000     -0.698307000000      0.000000000000
C    -1.209503000000      0.698307000000      0.000000000000
H     2.150882000000      1.241812000000      0.000000000000
H     2.150882000000     -1.241812000000      0.000000000000
H     0.000000000000     -2.483625000000      0.000000000000
H    -2.150882000000     -1.241812000000      0.000000000000
H    -2.150882000000      1.241812000000      0.000000000000
*

*tail_a
*

*tail_b
*

Phase behaviour: starts with GDIIS, switches to GEDIIS when rms_grad ≤ gediis_switch_rms (0.005 Ha/Å), then back to GDIIS for the final quadratic convergence when rms_disp < gediis_switch_step (0.001 Å).

Example 3 — GDIIS_blend with Trust Radius

Uses the blend optimizer with the fixed_sequential blend mode and a live trust radius. Suitable when the default GDIIS takes excessively large or oscillating steps.

nprocs = 10
mem = 40GB
method = n b3lyp/6-31g**
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = gaussian

# --- optimizer ---
use_gediis = blend
use_hybrid_gediis = true
gediis_blend_mode = fixed_sequential

*geom
C     0.000000000000      1.396613000000      0.000000000000
C     1.209503000000      0.698307000000      0.000000000000
C     1.209503000000     -0.698307000000      0.000000000000
C     0.000000000000     -1.396613000000      0.000000000000
C    -1.209503000000     -0.698307000000      0.000000000000
C    -1.209503000000      0.698307000000      0.000000000000
H     2.150882000000      1.241812000000      0.000000000000
H     2.150882000000     -1.241812000000      0.000000000000
H     0.000000000000     -2.483625000000      0.000000000000
H    -2.150882000000     -1.241812000000      0.000000000000
H    -2.150882000000      1.241812000000      0.000000000000
*

*tail_a
*

*tail_b
*

Blend behaviour: 50 % GDIIS + 50 % EDIIS far from convergence, transitions to pure GDIIS for the final steps. Trust radius contracts when energy rises and expands when energy falls.

Note: blend mode requires a direct Hessian method (hessian = direct_psb, bofill, powell, or bfgs_powell_mix). inverse_bfgs is incompatible.

Real-World Example — Cu Complex with Solvent

For a larger, more demanding system the to-4-tep-1 examples in examples/gaussian/ show a 29-atom Cu complex optimised at the ωB97X-D/def2-SVP level with SMD solvation in benzene:

nprocs = 48
mem = 190GB
method = n scf(maxcycle=300,xqc) UWB97XD/DEF2SVPP scrf(smd,solvent=Benzene)
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = gaussian
use_gediis = blend
use_hybrid_gediis = true
gediis_blend_mode = fixed_sequential

The geometry is read from the external file to-4-tep-1-blend-gdiis.xyz (included in the repository) via *geom\n@to-4-tep-1-blend-gdiis.xyz\n*.