# Input and Output

## Structure of the input

Everything that comes after the "!" is called the main input, and if specific options are necessary, they will be usually set in a section initiated by a % symbol and closed by and END.

Suppose, in the water case, one wants to increase the maximum number of SCF iterations to 500, then the input should be:

!HF DEF2-SVP
%SCF
MAXITER 500
END
* xyz 0 1
O   0.0000   0.0000   0.0626
H  -0.7920   0.0000  -0.4973
H   0.7920   0.0000  -0.4973
*


The main input can also be split over many lines, for the sake of readability, for instance:

!HF
!DEF2-SVP
%SCF
MAXITER 500
END
* xyz 0 1
O   0.0000   0.0000   0.0626
H  -0.7920   0.0000  -0.4973
H   0.7920   0.0000  -0.4973
*


For a complete discussion of all the main keywords and options, check the ORCA manual (must be logged in to access).

Note

The input reader is not case-sensitive. UPPER CASE, lower case, or aNy cOMmBINAtiON are allowed.

### Structure section

After the main input and options, comes the structure section, separated by stars. You can input the coordinates in Cartesian form, using the "xyz" flag or in Internal coordinates, using "int". Then come the system's charge and multiplicity ($$2S+1$$).

For a hydroxide radical ($$S=1/2$$) in internal coordinates, one input could be like:

!HF DEF2-SVP
* int 0 2
O  0 0 0 0.0    0.0 0.0
H  1 0 0 0.9903 0.0 0.0
*


Note

The atoms can be chosen by their symbol (H, C, Cu, Te) or by atomic number (1, 6, 29, 52), and the coordinates must be in Ångström.

The geometry can also be read from an external .xyz file using the "xyzfile" flag. In the previous case, if one had a "hydroxide.xyz" file in the same folder as the input, the input would be:

!HF DEF2-SVP
* xyzfile 0 2 hydroxide.xyz


In this case, there is no need to close the section with a second star below. The "hydroxide.xyz" should look like:

2

O  0 0 0
H  0 0 0.9903


It starts with the number of atoms, then comes a blank or comment line and then the structure - with coordinates in Angstroem.

## The output file

The first part of the output is a header with references to contributors and basis set information. After that come the WARNINGS, that should be carefully checked and:

****************************
* Single Point Calculation *
****************************


as a reference to the kind of calculation that will be performed. Then comes detailed information about the integral module (SHARK) and SCF parameters:

----------------------
SHARK INTEGRAL PACKAGE
----------------------

Number of atoms                             ...      2
Number of basis functions                   ...     19
Number of shells                            ...      9
Maximum angular momentum                    ...      2
Integral batch strategy                     ... SHARK/LIBINT Hybrid
RI-J (if used) integral strategy            ... SPLIT-RIJ (Revised 2003 algorithm where possible)
Printlevel                                  ...      1
Contraction scheme used                     ... SEGMENTED contraction

[...]

------------
SCF SETTINGS
------------
Hamiltonian:
Ab initio Hamiltonian  Method          .... Hartree-Fock(GTOs)
RI-approximation to the Coulomb term is turned on
Number of auxiliary basis functions  .... 371
RIJ-COSX (HFX calculated with COS-X)).... on

General Settings:
Integral files         IntName         .... teste
Hartree-Fock type      HFTyp           .... RHF
Total Charge           Charge          ....    0
Multiplicity           Mult            ....    1

[...]


Then the initial guess is built:

------------------------------
INITIAL GUESS: MODEL POTENTIAL
------------------------------
Calculating cut-offs                               ... done
Setting up the integral package                    ... done
Initializing the effective Hamiltonian             ... done
Starting the Coulomb interaction                   ... done (   0.0 sec)
Mapping shells                                     ... done
Starting the XC term evaluation                    ... done (   0.0 sec)
Transforming the Hamiltonian                       ... done (   0.0 sec)
Diagonalizing the Hamiltonian                      ... done (   0.0 sec)
Back transforming the eigenvectors                 ... done (   0.0 sec)
Now organizing SCF variables                       ... done


and if the SCF converges, you will see a message, together with a discrimination of the energy components:

            *****************************************************
*                     SUCCESS                       *
*           SCF CONVERGED AFTER   8 CYCLES          *
*****************************************************

----------------
TOTAL SCF ENERGY
----------------

Total Energy       :          -75.95933513 Eh           -2066.95859 eV

Components:
Nuclear Repulsion  :            9.06276654 Eh             246.61041 eV
Electronic Energy  :          -85.02210166 Eh           -2313.56901 eV
One Electron Energy:         -122.82422006 Eh           -3342.21694 eV
Two Electron Energy:           37.80211839 Eh            1028.64794 eV

Virial components:
Potential Energy   :         -151.67568240 Eh           -4127.30515 eV
Kinetic Energy     :           75.71634727 Eh            2060.34656 eV
Virial Ratio       :            2.00320919


The orbitals energies are printed, along with information on charges and timings. If some other method is required, such as MP2 or TD-DFT, it will appear next and the final calculated energy is printed as:

-------------------------   --------------------
FINAL SINGLE POINT ENERGY       -75.324154395464
-------------------------   --------------------


after which the dipole moment for the system is printed and the file ends.

## Visualization programs

If you want to visualize the data using a graphical user interface, there are many programs you can find online. Here, we cite three of them:

With these you can visualize your geometry, the charges, plot orbital diagrams or spectra and so on.

Important

It might be necessary to include some extra printing for these programs (e.g., to generate orbital plots). In that case, use LARGEPRINT on the main input:

!HF DEF2-SVP LARGEPRINT


and a very detailed output file will be printed with the necessary information.