GAUSSIAN

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GAUSSIAN is a computational chemistry software program, first written by John Pople and released in 1970. According to the manual, it can deal with different computational approaches: molecular mechanics (AMBER, UFF, DREIDING), semi-empirical calculations (AM1,PM3,CNDO,INDO,MINDO/3,MNDO), SCF methods (Restricted, Unrestricted, and Restricted Open-shell Hartree-Fock), Møller-Plesset perturbation theory, DFT methods (Hybrid functionals, exchange functionals and correlation functionals), ONIOM (QM/MM method), Complete Active Space (CAS) and Multi-Configurational Self-Consistent Field calculations, Coupled Cluster calculations, QCI methods and Quantum chemistry composite methods.

Installing Gaussian in your local computer

It is sometimes useful to be able to run short calculations on your local machine. Although this should not be done systematically to avoid burning out the machine. One option is to compile the code (painful). Another option is to copy a pre-compiled version following the instructions below. It will not run optimally for your machine, but ...

Installing Gaussian on your local computer

Gaussian for beginners

If you are not familiar with Gaussian and Gaussview, it might be a good idea to run some "simple" calculations before starting your "own" project. Following the ling below you will find some exercices prepared for the Master on Computational Chemistry, which are a good starting point.

Gaussian4beginners

Links

http://www.gaussian.com/tech_top_level.htm

http://en.wikipedia.org/wiki/GAUSSIAN

Gaussian related Tips:

ABOUT SENDING CALCULATIONS :

• Checkpoints: They are big files which contain information such as the wave function or the geometry of finished calculations. They can not be edited with vi or nedit... (as they are written in binary) but the information they contain can be read by Gaussian. Although they might be very useful, to store them is not recommended if we are not sure about their utility.

By default they are saved in the same directory where the output is saved. For practical reasons in the calculations sent to kimik the checkpoint file should be saved in the Scrath. To do so, you just need to write in the input:

   %chk=/scratch/namecheckpoint.chk

ABOUT NBO: Natural Bond Orbital Analysis

It is recommended to use the keyword pop=nboread in the command line and at the end of the file $NBO 3CBONDS RESONANCE $END

http://www.chem.wisc.edu/~nbo5/ch3nh2.html

ABOUT PCM (CPCM, IPCM,..) :

• If you have one or more hydrogens "bonded" to two atoms (close to two atoms), the default parameters of PCM will not be able to compute the molecular cavity for them. There are two solutions for this problem:

-1- Use a different model to build up the cavity. Change the default UAO which does not explicitly consider hydrogens, by UHF, PAULING, BONDING.. which consider hydrogens explicitly.

-2- Use the keyword SPHEREONH = atom number of the hydrogen "bonded" to two atoms.

• An odd tip about PCM: If your PCM calculations work fine for most of your systems but they give problems to compute the cavity for few of them, with no apparent reason: try to modify slightly your coordinates.

A very small change of the coordinates may be enough to eliminate the problem. A good way to do that is to round the coordinates (i.e. from 2.347895 to 2.348) or re-optimize the molecule (the coordinates you will get will be slightly different). Even though that sounds quite stupid some times it is enough for the program to work.