.. _orca:

====
ORCA
====

.. contents:: In this section:
   :local:
   :depth: 2

Description
===========

According to the `page of ORCA <https://www.faccts.de/orca/>`_, ORCA is a quantum chemistry software package that provides advanced methods in density functional theory (DFT) and correlated wavefunction methods. It is widely used in computational chemistry.

Available Versions
==================

* orca/4.0.1 (default)
* orca/4.2.1
* orca/5.0.3
* orca/5.0.4
* orca/6.0.0
* orca/6.0.1
* orca/6.1.0

Loading the Module
==================

.. code-block:: bash

   # Load ORCA
   module load orca/6.1.0

   # Verify installation
   orca --version

Serial Job Submission
=====================

.. code-block:: bash
   :caption: submit_orca_serial.sh

   #!/bin/bash
   #SBATCH -J orca_serial
   #SBATCH -N 1
   #SBATCH -n 1
   #SBATCH -t 24:00:00
   #SBATCH --mem=8G

   export INPUT="water.inp"
   export OUTPUT="water.out"

   module load orca/6.1.0

   job-nanny orca water.inp

Parallel Job Submission (OpenMP)
================================

.. code-block:: bash
   :caption: submit_orca_omp.sh

   #!/bin/bash
   #SBATCH -J orca_omp
   #SBATCH -N 1
   #SBATCH -c 8
   #SBATCH -t 48:00:00
   #SBATCH --mem=32G

   export INPUT="benzene.inp"
   export OUTPUT="benzene.out"

   module load orca/6.1.0

   # ORCA automatically uses threads
   job-nanny orca benzene.inp

.. note::
   The number of threads must be specified in the ORCA input file using the ``%pal nprocs`` directive.

MPI Job Submission
==================

.. code-block:: bash
   :caption: submit_orca_mpi.sh

   #!/bin/bash
   #SBATCH -J orca_mpi
   #SBATCH -N 2
   #SBATCH --ntasks-per-node=14
   #SBATCH -t 72:00:00
   #SBATCH --mem-per-cpu=4G

   export INPUT="large.inp"
   export OUTPUT="large.out"

   module load orca/6.1.0
   module load openmpi/4.1.8

   # ORCA calls mpirun internally - do not use mpirun explicitly
   job-nanny $ORCA_BIN large.inp

.. important::
   ORCA manages MPI execution internally. Do not use ``mpirun`` directly — just use ``$ORCA_BIN large.inp``. The number of processes must be specified in the input file.

It is possible that **Orca** may fail when using MPI parallelization with 2 or more nodes. In this case, a possible solution would be to create a file containing the node names using the command ``srun hostname -s | sort -u > hosts.$SLURM_JOB_ID``:

.. code-block:: bash
   :caption: submit_orca_mpi.sh

   #!/bin/bash
   #SBATCH -J orca_mpi
   #SBATCH -N 2
   #SBATCH --ntasks-per-node=14
   #SBATCH -t 72:00:00
   #SBATCH --mem-per-cpu=4G

   export INPUT="large.inp"
   export OUTPUT="large.out"

   module load orca/6.1.0
   module load openmpi/4.1.8

   srun hostname -s | sort -u > hosts.$SLURM_JOB_ID

   # ORCA calls mpirun internally - do not use mpirun explicitly
   job-nanny $ORCA_BIN large.inp

Example Input File
==================

.. code-block:: text
   :caption: water.inp

   ! RHF SVP OPT

   %pal
     nprocs 8  ! Number of threads/processes
     end

   %base "water"

   * xyz 0 1
   O    0.000000    0.000000    0.000000
   H    0.000000    0.757000    0.586000
   H    0.000000   -0.757000    0.586000
   *

DFT Calculation with Optimization
=================================

.. code-block:: bash
   :caption: submit_orca_dft.sh

   #!/bin/bash
   #SBATCH -J orca_dft
   #SBATCH -N 1
   #SBATCH -c 8
   #SBATCH -t 48:00:00
   #SBATCH --mem=32G

   export INPUT="dft_opt.inp"
   export OUTPUT="dft_opt.out"

   module load orca/6.1.0

   job-nanny orca dft_opt.inp

.. code-block:: text
   :caption: dft_opt.inp

   ! B3LYP DEF2-TZVP OPT FREQ

   %pal
     nprocs 8
     end

   %maxcore 4000

   %scf
     maxiter 500
     tole 1e-6
     end

   * xyz 0 1
   C    0.000000    0.000000    0.000000
   C    1.400000    0.000000    0.000000
   H   -0.550000    0.940000    0.000000
   H   -0.550000   -0.940000    0.000000
   H    1.950000    0.940000    0.000000
   H    1.950000   -0.940000    0.000000
   *

Properties Calculation (NMR, TD-DFT)
====================================

.. code-block:: bash
   :caption: submit_orca_props.sh

   #!/bin/bash
   #SBATCH -J orca_props
   #SBATCH -N 1
   #SBATCH -c 8
   #SBATCH -t 36:00:00
   #SBATCH --mem=32G

   export INPUT="nmr.inp"
   export OUTPUT="nmr.out"

   module load orca/6.1.0

   job-nanny orca nmr.inp

.. code-block:: text
   :caption: nmr.inp

   ! B3LYP DEF2-TZVP NMR

   %pal
     nprocs 8
     end

   %eprnmr
     nuclei = all C {shift}
     nuclei = all H {shift}
     end

   * xyz 0 1
   C    0.000000    0.000000    0.000000
   H    1.089000    0.000000    0.000000
   H   -0.363000    1.026000    0.000000
   H   -0.363000   -0.513000   -0.889000
   H   -0.363000   -0.513000    0.889000
   *

.. code-block:: text
   :caption: td.inp

   ! B3LYP DEF2-TZVP TDDFT

   %pal
     nprocs 8
     end

   %tddft
     nroots 10
     end

   * xyz 0 1
   C    0.000000    0.000000    0.000000
   C    1.400000    0.000000    0.000000
   H   -0.550000    0.940000    0.000000
   H   -0.550000   -0.940000    0.000000
   H    1.950000    0.940000    0.000000
   H    1.950000   -0.940000    0.000000
   *

Job Array for Parameter Scan
============================

.. code-block:: bash
   :caption: submit_orca_array.sh

   #!/bin/bash
   #SBATCH -J orca_array
   #SBATCH --array=1-5
   #SBATCH -N 1
   #SBATCH -c 8
   #SBATCH -t 24:00:00
   #SBATCH --mem=16G

   PARAMS=(
       "B3LYP"
       "PBE0"
       "M06"
       "wB97X"
       "TPSS"
   )

   METHOD=${PARAMS[$SLURM_ARRAY_TASK_ID-1]}
   export INPUT="template.inp"
   export OUTPUT="${METHOD}/"

   module load orca/6.1.0

   mkdir -p ${METHOD}
   cd ${METHOD}

   # Modify method in input file
   sed "s/FUNCTIONAL/${METHOD}/g" ../template.inp > input.inp

   job-nanny orca input.inp

Results Analysis
================

.. code-block:: bash
   :caption: analyze_orca.sh

   #!/bin/bash
   #SBATCH -J analyze_orca
   #SBATCH -N 1
   #SBATCH -n 1
   #SBATCH -t 00:30:00
   #SBATCH --mem=2G

   # Extract final energy
   grep "FINAL SINGLE POINT ENERGY" *.out | awk '{print $6}' > energies.txt

   # Extract optimized geometry
   for out in *.out; do
       echo "Optimized geometry for $out:" >> optimized.txt
       awk '/CARTESIAN COORDINATES/,/CARTESIAN COORDINATES/ {
           if(NF==4 && $1!="CARTESIAN") print $0
       }' $out >> optimized.txt
       echo "" >> optimized.txt
   done

   # Extract vibrational frequencies
   grep "FREQUENCIES IN CM" -A 5 *.out > frequencies.txt

   # Extract HOMO/LUMO orbitals
   grep "HOMO" *.out | awk '{print $3, $5}' > homo_lumo.txt

   # Extract gaps
   grep "GAP" *.out | awk '{print $3}' > gaps.txt

   # Extract excitation times (TD-DFT)
   grep "STATE" *.out | grep -v "TOTAL" > excitations.txt

References
==========

- Documentation: https://www.faccts.de/orca/
- Manuals: https://www.faccts.de/docs/orca/
- Forum: https://orcaforum.kofo.mpg.de/

.. seealso::

   - :ref:`gamess` - Ab initio quantum chemistry
   - :ref:`gaussian` - Commercial quantum chemistry
   - :ref:`running_simulations` - How to submit jobs