Gaussian 03 input consists of a series
of lines in an ASCII text file. The basic structure of a Gaussian input
file includes several different sections:
Link 0 Commands:
Locate and name scratch files (not blank line terminated).
section (# lines): Specify desired calculation type, model
chemistry and other options (blank line terminated).
section: Brief description of the calculation (blank line terminated).
specification: Specify molecular system to be studied (blank line terminated).
additional sections: Additional input needed for specific job types
(usually blank line terminated).
Many Gaussian 03
jobs will include only the second, third, and fourth sections. Here is an example
of such a file, which requests a single point energy calculation on water:
# HF/6-31G(d) Route section
water energy Title section
0 1 Molecule specification
O -0.464 0.177 0.0
H -0.464 1.137 0.0
H 0.441 -0.143 0.0
In this job, the route and title sections each consist of a single line.
The molecule specification section begins with a line giving the charge and spin
multiplicity for the molecule: 0 charge (neutral molecule) and spin multiplicity
1 (singlet) in this case. The charge and spin multiplicity line is followed by
lines describing the location of each atom in the molecule; this example uses
Cartesian coordinates to do so. Molecule specifications are discussed in more
detail later in this chapter.
The following input file illustrates the use
of Link 0 commands and an additional input section:
%Chk=heavy Link 0 section
#HF/6-31G(d) Opt=ModRedundant Route section
Opt job Title section
0 1 Molecule Specification section
atomic coordinates …
3 8 Add a bond and an angle to the internal
2 1 3 coordinates used during the geom. opt.
This job requests a geometry optimization.
The input section following the molecule specification is used by the Opt=ModRedundant
keyword, and it serves to add an additional bond and angle in the internal coordinates
used in the geometry optimization. The job also specifies a name for the checkpoint
Link 0 commands were introduced in the last chapter and are discussed
individually in the penultimate section of this chapter. The remaining input sections
are discussed in the subsequent subsections of this introductory section. For
convenience, the table below lists all possible sections that might appear within
a Gaussian 03 input file, along with the keywords associated with
In general, Gaussian input is subject
to the following syntax rules:
Input is free-format and case-insensitive.
tabs, commas, or forward slashes can be used in any combination to separate items
within a line. Multiple spaces are treated as a single delimiter.
to keywords may be specified in any of the following forms:
keyword = option
keyword=(option1, option2, ...)
keyword(option1, option2, ...)
Multiple options are enclosed in parentheses
and separated by any valid delimiter (commas are conventional and are shown above).
The equals sign before the opening parenthesis may be omitted, or spaces may optionally
be included before and/or after it.
Note that some options also
take values; in this case, the option name is followed by an equals sign: for
All keywords and options
may be shortened to their shortest unique abbreviation within the entire Gaussian
03 system. Thus, the Conventional option to the SCF keyword
may be abbreviated to Conven, but not to Conv (due to the presence
of the Convergence option). This holds true whether or not both Conventional
and Convergence happen to be valid options for any given keyword.
contents of an external file may be included within a Gaussian 03
input file using the following syntax: @filename. This causes the entire
file to be placed at the current location in the input stream. Appending /N
to such commands will prevent the included file's contents from being echoed at
the start of the output file.
Comments begin with an exclamation
point (!), which may appear anywhere on a line. Separate comment lines
may appear anywhere within the input file.
Gaussian 03 Input
blank line? |
|Link 0 commands||% commands||no|
|Route Section (# lines)||all||yes|
||Geom=Connect or ModConnect
|Modifications to coordinates
|2nd title and molecule specification||Opt=QST2
set of coordinates
|Geom=Connect or ModConnect
and QST2 or QST3
|Modifications to 2nd set of coordinates
||Opt=ModRedun and QST2 or QST3
|3rd title and initial
TS structure||Opt=QST3||yes for both|
|Connectivity specifications for 3rd |
set of coordinates
|Geom=Connect or ModConnect
|Modifications to 3rd set of coordinates
|Frequency of interest
|Molecular Mechanics parameters
||HardFirst, SoftFirst, SoftOnly, Modify
|Initial force constants (Cartesian)||Opt=FCCards||yes|
|Accuracy of energy & forces||Opt=ReadError||no|
|BOMD/ADMP input (1 or more sections)||ADMP
set specification||Gen, GenECP,
|Finite field coefficients
|Density fitting basis set specification
||Extra Density Basis
|Background charge distribution||Charge||yes|
|Symmetry types to combine||Guess=LowSymm||no|
|Orbital specifications (separate α & β)||Guess=Cards||yes|
|Orbital alterations (separate α & β)||Guess=Alter||yes|
|Orbital reordering (separate α & β)||Guess=Permute
|PCM solvation model input||SCRF=Read||yes|
|Weights for CAS state averaging||CASSCF=StateAverage||no|
|States of interest for spin orbit coupling||CASSCF=Spin||no|
|# Orbitals/GVB pair||GVB||no|
|Atoms list for spin-spin coupling constants
|Alternate atomic radii||Pop=ReadRadii
|Data for electrostatic properties||Prop=Read
(& Cards input)||Cube||yes|
|Orbital freezing information||ReadWindow
|OVGF orbitals to refine||OVGF=ReadOrbitals||yes|
|Temperature, pressure, atomic masses||Freq=ReadIsotopes||no|
|PROAIMS/Pickett output filename||Output=WFN
to go on to the next section.