Gaussian 09 Input Overview

Gaussian 09 input consists of a series of lines in an ASCII text file. The basic structure of a Gaussian input file includes several different sections:

Many Gaussian 09 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 file.

For convenience, the following table all possible sections that might appear within a Gaussian 09 input file, along with the keywords associated with each one.

Gaussian 09 Input Section Ordering

SectionKeywordsFinal blank line?
Link 0 commands% commandsno
Route Section (# lines)allyes
Extra OverlaysExtraOverlaysyes
Title sectionall except Geom=AllCheckyes
Molecule specificationall except Geom=AllCheckyes
Connectivity specificationsGeom=Connect or ModConnectyes
Alterations to frozen atomsGeom=ReadFreezeyes
Modifications to coordinatesOpt=ModRedundantyes
2nd title and molecule specificationOpt=QST2 or QST3yes for both
Connectivity specs. for 2nd set of coordinatesGeom=Connect or ModConnect and Opt=QST2 or QST3yes
2nd Alterations to frozen atomsGeom=ReadFreezeyes
Modifications to 2nd set of coordinatesOpt=QST2 or QST3yes
3rd title and initial TS structureOpt=QST3yes for both
Connectivity specs. for 3rd set of coordinatesGeom=Connect or ModConnect Opt=(ModRedun, QST3)yes
3rd Alterations to frozen atomsGeom=ReadFreezeyes
Modifications to 3rd set of coordinatesOpt=(ModRedun, QST3)yes
PDB secondary structure informationautomatic if residue info in molecule specificationyes
Atomic massesReadIsotopes optionyes
Molecular Mechanics parametersHardFirst, SoftFirst, SoftOnly, Modifyyes
Frequency of interestCPHF=RdFreqyes
Background charge distributionChargeyes
BOMD/ADMP input (1 or more sections)ADMP and BOMD required input and ReadVelocity, ReadMWVelocity optionsyes
PCM inputSCRF=(ExternalIteration,Read)yes
Coordinates for IRC tableIRC=Reportyes
Harmonic constraintsGeom=ReadHarmonicyes
Semi-empirical parameters (Gaussian format)Input option, AM1=Bothyes
Semi-empirical parameters (MOPAC format)MOPAC, Both optionsyes
Basis set specificationGen, GenECP, ExtraBasisyes
Basis set alterationsMassageyes
Finite field coefficientsField=Readyes
ECP specificationPseudo=Cards, GenECPyes
Density fitting basis set specificationExtraDensityBasisyes
PCM solvation model inputSCRF=Readyes
DFTB parametersDFTByes
Source for initial guessGuess=Inputyes
Symmetry types to combineGuess=LowSymmno
Orbital specifications (separate α & β)Guess=Cardsyes
Orbital alterations (separate α & β)Guess=Alteryes
Orbital reordering (separate α & β)Guess=Permuteyes
# Orbitals/GVB pairGVBno
Weights for CAS state averagingCASSCF=StateAverageno
States of interest for spin orbit couplingCASSCF=SpinOrbitno
Orbital freezing informationReadWindow optionsyes
EPT orbitals to refineEPT=ReadOrbitalsyes
Atoms list for spin-spin coupling constantsNMR=ReadAtomsyes
Alternate atomic radiiPop=ReadRadii or ReadAtRadiiyes
Data for electrostatic propertiesProp=Read or Optyes
NBO inputPop=NBOReadno
Harmonic Normal Mode selectionFreq=SelectNormalModesyes
Hindered Rotor inputFreq=ReadHinderedyes
Anharmonic Normal Mode selectionFreq=SelectAnharmonicNormalModesyes
Normal Modes for FCHTFreq=SelectFCHTNormalModesyes
Input for AnharmonicFreq=ReadAnharmonicyes
Input for FCHTFreq=ReadFCHTyes
Pickett output filenameOutput=Pickettno
PROAIMS output filenameOutput=WFNno

Input Syntax

In general, Gaussian input is subject to the following syntax rules:


Last updated on: 10 May 2009