ORCA 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.

ORCA memory: pass the MaxCore value in MB, not the total job memory. For example, mem = 4000 means 4 000 MB per core.

Example 1 — Default GDIIS

nprocs = 10
mem = 4000
method = B3LYP 6-31G(d,p) VeryTightSCF
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = orca
orca_comm = orca

*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: default GDIIS, hessian = direct_psb, switch_step = 3.

On HPC systems, set orca_comm to the full path of the ORCA binary, e.g.:

orca_comm = /apps/orca/6.1.1/orca

Example 2 — GDIIS_blend with Gradient-Based Weight

Uses use_gediis = blend with gediis_blend_mode = gradient. The blend weight $w$ varies smoothly as $w={\text{RMS}}_g/({\text{RMS}}_g+\text{switch\_rms})$, so the optimizer is EDIIS-heavy far from convergence and GDIIS-heavy close to it.

nprocs = 10
mem = 4000
method = B3LYP 6-31G(d,p) VeryTightSCF
charge = 1
mult_a = 3
mult_b = 1
mode = normal
program = orca
orca_comm = orca

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

*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
*

TD-DFT with State Selection

For excited-state MECPs, add %tddft blocks in the tail sections and set state_a / state_b to select which excited state to track:

nprocs = 10
mem = 4000
method = B3LYP def2-SVP VeryTightSCF
charge = 0
mult_a = 1
mult_b = 1
state_a = 1
state_b = 2
mode = normal
program = orca
orca_comm = orca

*geom
...
*

*tail_a
%tddft
  nroots 5
  iroot 1
end
*

*tail_b
%tddft
  nroots 5
  iroot 2
end
*