General Input

ORCA both has a Simple keyword syntax as well as a Block syntax. The Simple input is often the only inputline needed (as well as the coordinates block) while some specific settings are only available using the Block Input. Note that settings specified in the Block input always takes precedence over the Simple input.

ORCA Input files are pretty much free-format. Blank lines are allowed, input is usually not case-sensitive. One can create comment lines by adding the  "#" symbol to a line.

Simple input

In the Simple input syntax, keywords are added in any order to the line beginning with "!". Multiple "!" lines are also allowed.

! Keyword1 Keyword2 Keyword3 

# Comment lines can be added if the line begins with a #.

The geometry block is the only other strict requirement to the inputfile (see Geometry Input also). Here shown for a calculation on the H2 molecule with charge 0, spin multiplicity of 1 and Cartesian coordinates (in Å) for the 2 H atoms: 

*xyz 0 1
H 0.0 0.0 0.0
H 0.0 0.0 1.0
*

Job types are typically specified using a Simple input keyword. The default job is a single-point energy evaluation (same as Energy or SP) and does not need to be specified explicitly (but method and basis set must be).

• If a geometry optimization is requested, the Opt keyword is added to the Simple Input line: !Opt  (See Geometry optimizations)

• If an energy+gradient evaluation is requested: !EnGrad

• If vibrational frequencies are wanted: !Freq (See Vibrational Frequencies & Thermochemistry)

• If molecular dynamics is wanted: !MD (See Molecular dynamics)

Example input:

! B3LYP def2-SVP Opt
# B3LYP is here the method (DFT functional), def2-SVP the basis set and Opt is the jobtype (geometry optimization).
# Order of the keywords is not important.

*xyz 0 1
H 0.0 0.0 0.0
H 0.0 0.0 1.0
*

Block input

Advanced settings are often specified using the Block input for different modules. Blocks start with "%nameofblock" and end with "end". Note that settings specified in the Block input always takes precedence over the Simple input. Hence you can override settings from the Simpleinput line.

!
%block
block-specific keywords
end

For example, changing the maximum number of SCF iterations requires creating the SCF block and adding SCF-block specific keywords:

!
%scf
MaxIter 100
end 

Or requesting a 10-root TDDFT calculation (that is performed after the ground-state DFT calculation):

! BP86 def2-SVP def2/J

%scf
maxiter 100
end 

%tddft
nroots 10
end 

Multiple input job

For a multiple input job, you can either use the $new_job feature or the compound-method feature. Note that the  $new_job feature is an old feature of ORCA that may be eventually be removed from ORCA. The compound-method feature is the modern way of doing multi-step workflows in ORCA

compound-method feature

See manual for information on how to use.
It will not be documented here.

Compounds scripts repository

$new_job feature

When using the $new_job feature %base labels are necessary to distinguish each job from each other. Note also that ORCA will automatically load the orbitals from the previous jobs and use instead of the standard guess, potentially saving time (use NoAutostart to prevent this).

If you want to run multiple single-point calculations on the same geometry. 

! BP86 def2-SVP def2/J xyzfile
%base "bp86"
*xyz 0 1
coordinates
*

$new_job

! B3LYP def2-SVP NORI
%base"b3lyp"
*xyzfile 0 1

If you want to run a geometry optimization followed by one or more single-point calculations:

! BP86 def2-SVP def2/J xyzfile Opt
%base "bp86opt"
*xyz 0 1
coordinates
*
$new_job
! B3LYP def2-TZVP NORI
%base"b3lypsp"
*xyzfile 0 1

If you want to run multiple calculations on multiple xyz files:

! BP86 def2-SVP def2/J NOAUTOSTART
*xyzfile -1 4 C-.xyz
$new_job
! BP86 def2-SVP def2/J NOAUTOSTART
*xyzfile 0 3 C.xyz
$new_job
! BP86 def2-SVP def2/J NOAUTOSTART
*xyzfile -1 1 Cl-.xyz
$new_job
! BP86 def2-SVP def2/J NOAUTOSTART
*xyzfile 0 2 Cl.xyz