Anatomy of an input file¶
Below is an example of an input file from the HF tutorial with some extra comments.
system name: H2O charge: 0 end system !A comment do ground state end do !Another comment method hf !A third comment end method geometry basis: cc-pVDZ H 0.86681 0.60144 0.00000 H -0.86681 0.60144 0.00000 O 0.00000 -0.07579 0.00000 end geometry
The input consists of a set of sections. A section begins with the name of the section and ends with an end statement.
section name ... end section name
In the example input above, the
geometry sections are given. These four sections are needed in every input.
The program will do a sanity check of the input, and throw an error if it detects a nonexisting section. See here for a list of all sections and keywords.
Keywords are placed in the sections:
section name keyword 1: value keyword 2 end section name
Many keywords have default values and are not required unless you don’t want the default. A few keywords are always required. In general, the set of required keywords and sections will depend on the type of calculation.
Some keywords require a value.
These keywords are followed by
: and then the value:
keyword 1: value
do not require a value, e.g.
ground state in the example above.
The input file is not case sensitive.
Whitespaces can be added, for instance to add indentation to your input file. Lines can be commented out using
! (except in the
geometry section). Blank lines between sections are ignored.
The geometry section must be the final section in the input.