Gaussian input file

The route section of a Gaussian input file specifies the kind of job you want to run as well as the specific theoretical method and basis set which should be used. All of these items are specified via keywords. Recall that the first line of the route section begins with a sign (or T to request terse output). 

Note that the separate input sections are separated from one another by blank lines. These blank lines are inserted automatically into input files created with the Job Entry window in the Windows version and need not be entered by the user. If you choose to create a Gaussian input file using an external Windows editor, however, you must follow the same rules for input as under other versions of Gaussian. 

Appendix B, Overview of Gaussian Input, provides a summary of the Gaussian input file format. It also discusses techniques for creating Z-matrix representations of moleailar systems. 

Next, we ll prepare a Gaussian input file for an energy calculation on water. 

This command will create a new Gaussian input file. NewZMat may prompt you for the charge and multiplicity to use accept the default values offered. 

The title section of a Gaussian input file contains a brief (usually one-line) description of the job. Enter something like the following into this section ... 

This directs the program to save the input you typed in to a file. Select the desired directory location in the standard Windows save dialog box, and give the input file the name H20.GJF. GJF is the extension used for Gaussian input files on Windows systems (standing for Gaussian fob File). 

Load existing Gaussian input file or convert o molecular structure. 

As a somewhat more complex example, let us now consider the case of ozone (O3), which has an open-shell singlet ground state (Sidebar 3.2). The Gaussian input file to obtain the open-shell wavefunction and default NBO analysis for experimental equilibrium geometry Roo= 1-272, 0= 116.8 ) is shown below. 

A sample Gaussian input file to perform the formamide NOSTAR optimization is shown below ... 

Many polyatomic molecules possess the interesting ability to induce a dipole moment in a direction (say, y) perpendicular to the applied electric field (say, x), corresponding to nonvanishing cc y polarizability component. Consider the simple triatomic species HN=0, with N=0 along the horizontal x axis, and with a finite electric field of strength 0.001 a.u. in the x-direction, as shown in the Gaussian input file below ... 

A Gaussian input file to evaluate the reoptimized Xj triad in the presence of an electric FIELD of strength 10 (multiples of 0.0001 a.u.) along the interatomic z-direction is shown below for X=Li ... 

PracticalNote-. The following Gaussian input file will calculate the relaxed (geometry-optimized) potential curve for values of dist Rpp in the range 2.0. 0 A (in increments of 0.01 A) ... 

A sample Gaussian input file is shown in I/O-lO.l illustrating use of the QST3 method to find the optimized TSi ni for hydroxymethylene decomposition (10.8), with input specification of optimized structures for Rm, Pi and an initial guess... 

The corresponding Gaussian input file to find points along the intrinsic reaction coordinate (IRC) for reaction in (10.8) and (10.9) is shown in 1/0-10.2. 

Gaussian input syntax for various CI/CAS methods can be illustrated for the simple case of vertical (fixed geometry) excitation to the first excited (/= 1) state of nitric oxide (NO). A sample Gaussian input file to evaluate and analyze the CIS wavefunction for this state at fixed Sao = 1.2 A is shown helow ... 

The excited states of NO can also be approximated by complete active space (CAS) calculations (Sidebar 11.2) employing NBOs as starting orbitals ( CAS/NBO method ). As an illustrative application we consider full-valence CAS(11,8) active space (with /V= 11 electrons, 8 orbitals) to optimize and analyze the nroot=6 (fifth excited root) of NO, as shown in the Gaussian input file below ... 

For NRT bond order calculations reported in Tables 11.2 and 11.3, we employ SNRTSTR keylists to force consistent inclusion of alternative single-, double-, and triple-bonded resonance structures in each state. A sample Gaussian input file to compute the final entries of Table 11.3 for the C-state at / = 1.60 A is given below ... 

Density = Current is specified. Pop = NOAB specifies that separate orbitals for spin up and spin down electrons should be written to the. wfx file. Since GAUSSIAN 09 Revision C, Density = Current is included by default. The desired name for the. wfx output file must be specified at the bottom of the GAUSSIAN input file. 

As an example, consider a coupled-cluster calculation of the ozone triplet state. The molecular geometry was optimized using the CCSD method with aug-cc-pVTZ basis sets, no frozen core electrons (full), and no symmetry constraints (NoSymm). (The keywords (full,SaveAmplitudes), scf=(fermi, maxcycle = 400), and geom = connectivity are convenient options but not required to run the calculation.) The file ozone triplet CCSD.wfx was written at the completion of the calculation. Below is an example GAUSSIAN input file for performing these tasks ... 

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