GAUSSIAN

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.

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 wich contain information such as the wavefunction or the geometry of finished calculations. They can not be edited with vi or nedit... but the information they contain can be readed by Gaussian. Although they might be very useful to store them if we are not sure about their utility is not recommended.

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

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.