Quick Start

This page walks through the two ways to set up a calculation and how to run it.

Option 1: Generate a Template (Recommended)

OpenMECP can generate a ready-to-edit input file from any existing geometry file.

# From an XYZ file
omecp ci molecule.xyz
# Creates: molecule.inp

# From a Gaussian output file
# (adds _omecp suffix to avoid overwriting your output)
omecp ci calculation.log
# Creates: calculation_omecp.inp

# From a Gaussian input file
omecp ci input.gjf
# Creates: input.inp

# Specify a custom output name
omecp ci molecule.xyz my_run.inp

Then open the generated .inp file and fill in the required keywords (program, method, nprocs, mem, charge, mult_a, mult_b).

Option 2: Write an Input File Manually

Create a file named input.inp with the following structure:

*geom
C     -4.108383   -0.269570   -0.105531
C     -3.086048   -0.004314   -0.907012
H     -4.464908    0.456695    0.621271
H     -4.622302   -1.226624   -0.151874
C     -2.326155    1.302381   -0.898892
H     -2.751025   -0.749763   -1.624593
H     -2.733108    1.996398   -0.159695
H     -1.274400    1.129883   -0.660641
H     -2.379567    1.780215   -1.879473
*

*tail_a
# Extra Gaussian route keywords for state A
*

*tail_b
# Extra Gaussian route keywords for state B
*

program  = gaussian
method   = B3LYP/6-31G*
nprocs   = 4
mem      = 4GB
charge   = 0
mult_a   = 1
mult_b   = 3

See the Input File Format chapter for the full section reference and the Keywords Reference for all available parameters.

Running OpenMECP

omecp input.inp > output.log

On an HPC cluster, put the above in a job submission script and load your QM program module before calling omecp.

Checking the Results

Built-in Help

OpenMECP includes a comprehensive built-in help system:

omecp --help               # General usage
omecp --help keywords      # All input keywords with descriptions
omecp --help methods       # Supported QM methods
omecp --help features      # Feature overview
omecp --help examples      # Worked examples
omecp ci --help            # Template generation help

Minimal Gaussian Example

*geom
Fe    0.000000    0.000000    0.000000
N     0.000000    0.000000    2.100000
N     0.000000    2.100000    0.000000
*

*tail_a
*

*tail_b
*

program  = gaussian
method   = B3LYP/def2-SVP
nprocs   = 8
mem      = 16GB
charge   = 0
mult_a   = 1
mult_b   = 3

Minimal ORCA Example

*geom
Fe    0.000000    0.000000    0.000000
N     0.000000    0.000000    2.100000
*

*tail_a
%scf
  MaxIter 500
end
*

*tail_b
*

program  = orca
method   = B3LYP def2-SVP
nprocs   = 8
mem      = 8000
charge   = 0
mult_a   = 1
mult_b   = 3