(sec:orcaarchitecture.general)=
# ORCA Structure

(sec:programs.general)=
## Program Components

The program system ORCA consists of several separate programs that call
each other during a run. The following basic modules are included in
this release (listed in alphabetical order):

:::{list-table}
* - orca
  - Main input+driver program
* - orca_ailft
  - Ab Initio Ligand Field Theory
* - orca_autoci
  - CI type program using the automated generation environment (ORCA-AGE)
* - orca_casscf
  - Main program for CASSCF driver
* - orca_casscfresp
  - CASSCF static linear response
* - orca_cclib
  - Precalculation of one particle coupling coefficients for ACCCI
* - orca_chelpg
  - Calculation of different kinds of ESP charges
* - orca_ciprep
  - Preparation of data for MRCI calculations (frozen core matrices and the like)
* - orca_cipsi
  - Iterative Configuration Expansion Configuration Interaction (ICE-CI)
* - orca_cis
  - Excited states via CIS and TD-DFT
* - orca_cisresp
  - CIS response calculation
* - orca_compound
  - General driver of the ORCA compound language
* - orca_crystalprep
  - Set up an embedding calculation from a crystal structure file
* - orca_eca
  - Auxiliary program for solving magnetic model Hamiltonians
* - orca_eda
  - Energy decomposition analysis module
* - orca_esd
  - Excited state dynamics program for calculating vibronic spectra, resonance Raman, ...
* - orca_grad
  - General gradient module
* - orca_guess
  - Generation of an intial guess for SCF and CASSCF
* - orca_leanscf
  - Self consistent field program for HF and DFT
* - orca_lft
  - Ligand Field Theory
* - orca_loc
  - Calculation of localized molecular orbitals
* - orca_mcrpa
  - CASSCF linear response for excited states
* - orca_md
  - Molecular dynamics program
* - orca_mdci
  - Matrix driven correlation program: CI, CEPA, CPF, QCISD, CCSD(T)
* - orca_mm
  - Classical forcefield components
* - orca_mp2
  - MP2 program (conventional, direct and RI)
* - orca_mrci
  - MRCI and MRPT calculations (individually selecting)
* - orca_ndoint
  - Calculates semiempirical integrals and gradients
* - orca_nmrspectrum
  - Simulates NMR spectra from calculated NMR parameters
* - orca_numfreq
  - Numerical Hessian computation
* - orca_pc
  - Addition of point charge terms to the one-electron matrix
* - orca_plot
  - Generation of orbital and density plots
* - orca_pop
  - External program for population analysis on a given density
* - orca_prop
  - Calculation of molecular properties
* - orca_propint
  - Calculation of property integrals
* - orca_rel
  - (Quasi) Relativistic corrections
* - orca_rocis
  - Excited states via the ROCIS method
* - orca_scfgrad
  - Analytic derivatives of SCF energies (HF and DFT)
* - orca_scfresp
  - self consistent field response
* - orca_startup
  - Calculation of startup data before each single point
* - orca_vpot
  - Calculation of the electrostatic potential on a given molecular surface
* - orca_vpt2
  - VPT2 analysis
:::