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Output Analysis

After executing the RHF calculation, ORCA produces several output files. The primary file, h2o_rhf.out, contains detailed information about the progress of the Self-Consistent Field (SCF) procedure, convergence behavior, molecular orbital energies, electronic properties, and the final Hartree–Fock energy.

This chapter explains the most important sections of the output file.

Program Header

The beginning of the output identifies the ORCA version and confirms that the calculation has started successfully.

******************************************
*             O   R   C   A              *
******************************************

Program Version 6.1.1

This section provides

  • ORCA version
  • compilation information
  • execution date and time
  • number of processors used

These details are useful for ensuring reproducibility, especially when comparing calculations performed using different ORCA versions.

Input Summary

Near the beginning of the output, ORCA echoes the input parameters used for the calculation.

Typical information includes

  • Hartree–Fock method
  • def2-SVP basis set
  • molecular charge
  • spin multiplicity
  • molecular geometry

Always verify this section before analyzing any results, as it confirms that ORCA interpreted the input correctly.

Basis Set Information

ORCA next constructs the atomic basis functions required for the Hartree–Fock calculation.

For the present calculation the output reports

Number of atoms          : 3
Number of Electrons      : 10
Number of Basis Functions: 24

The water molecule contains

  • 3 atoms
  • 10 electrons
  • 24 contracted basis functions using the def2-SVP basis.

These basis functions are used to build the molecular orbitals during the SCF procedure.

SCF Iterations

The most important part of the output is the SCF iteration table.

A typical section appears as

ITER       Energy              Delta-E          RMSDP
--------------------------------------------------------
...

During each iteration ORCA

  1. builds the Fock matrix,
  2. solves the Roothaan equations,
  3. constructs a new density matrix,
  4. checks whether self-consistency has been reached.

Several quantities are monitored throughout the iterations.

Quantity Meaning
Energy Total Hartree–Fock energy
Delta-E Energy change from previous iteration
RMSDP Root-mean-square density matrix change
MaxDP Maximum density matrix change

As the SCF converges,

  • the total energy stabilizes,
  • density matrix changes become very small,
  • convergence thresholds are eventually satisfied.

SCF Convergence

After a few iterations ORCA reports successful convergence.

SCF CONVERGED AFTER ...

This indicates that the electronic wavefunction is self-consistent and the molecular orbitals have been optimized.

Only after SCF convergence are the reported molecular properties physically meaningful.

Final RHF Energy

One of the most important quantities in the output is the final Hartree–Fock energy.

For this calculation

FINAL SINGLE POINT ENERGY

-75.960188531861

The same value is also recorded in the property file

Final Energy = -75.960188531861 Eh

This is the converged electronic energy of the water molecule at the supplied geometry using

  • Restricted Hartree–Fock
  • def2-SVP basis set

The value is expressed in Hartree (Eh).

Molecular Orbital Energies

Following SCF convergence, ORCA prints the molecular orbital energies.

A typical section contains

NO   OCC          E(Eh)
------------------------
...

Here

  • Occupied orbitals possess occupation number 2.000
  • Virtual orbitals possess occupation number 0.000

These orbital energies are frequently used to

  • identify the HOMO and LUMO,
  • estimate HOMO–LUMO gaps,
  • construct active spaces for subsequent CASSCF calculations.

Population Analysis

ORCA automatically performs several population analyses.

For the water molecule, the property file reports the following Mulliken charges.

Atom Mulliken Charge
O -0.3591
H +0.1795
H +0.1795

These values indicate electron density transfer from the hydrogen atoms toward the more electronegative oxygen atom.

The property file also contains Löwdin charges.

Atom Löwdin Charge
O -0.1487
H +0.0744
H +0.0744

Löwdin charges generally exhibit a weaker dependence on the basis set than Mulliken charges and often provide a more balanced description of atomic populations.

Mayer Bond Orders

The Mayer bond order analysis gives

Bond Bond Order
O–H 0.995
O–H 0.995

Bond orders close to one indicate that both O–H bonds possess essentially single-bond character, as expected for the water molecule.

Dipole Moment

The property file also reports the molecular dipole moment.

Dipole Magnitude = 0.79124 a.u.

The electronic and nuclear contributions are listed separately before ORCA computes the total molecular dipole.

Dipole moments are important for

  • infrared spectroscopy,
  • intermolecular interactions,
  • solvent models,
  • electrostatic potential calculations.

Calculation Summary

At the end of the property file ORCA summarizes the calculation.

Property Value
Charge 0
Multiplicity 1
Electrons 10
Atoms 3
Basis Functions 24
Final Energy -75.96018853 Eh
SCF Converged Yes

This section provides a concise overview of the completed calculation and confirms that the RHF procedure terminated successfully.

Generated Files

Several files are produced after the calculation.

File Purpose
h2o_rhf.out Complete output file
h2o_rhf.gbw Binary wavefunction containing molecular orbitals
h2o_rhf.densities Electron density information used by ORCA and visualization programs
h2o_rhf.property.txt Molecular properties including charges, bond orders, dipole moments, and energies

Among these, the GBW file is particularly important because it stores the converged molecular orbitals and serves as the starting point for subsequent calculations such as CASSCF, NEVPT2, and various excited-state methods.