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.

INFORMATION TO MERGE HERE!!!

G03

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 (potentially 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

Graphical Interfaces

link to the GaussView help : [[1]]

Input Examples

In spite of the highly informative Gaussian homepage, it can sometimes be difficult for newcomers to get a quick overview of the program. In order to make the introduction to the program easier, input examples for several kinds of calculations will be presented in the following. In this way users new to the program can just copy, paste and modify the input examples and they will have a calculation ready to submit.

Geometry optimisation

Constrained optimisation

Transition sate search

QST2 calculation

IRC calculation

Optimisation from transition state geometries

Issues related to the output

Structure of program execution

At the beginning of the output file there is a section describing the structure of the program execution. The numbers refer to which IOps that will be executed an in which order. A part from that, my knowledge on the topic is quite limited. The example below is from an ONIOM calculation and further down I have put some questions I would like you to answer.

1/6=70,8=5,10=4,14=-1,18=1000120,38=1,52=2,56=1,57=2,64=2/1,3;
 2/9=110,15=1,17=6,18=5,40=1/2;
 1/6=70,8=5,10=4,14=-1,18=1000120,38=1,52=2,53=3172,64=2/20;
 3/5=26,6=2,11=9,16=1,25=1,30=1/1;
 4/20=10,22=2,24=3,28=10/2;
 7/7=1,25=1,30=1,33=-1,44=-1/16;
 1/6=70,8=5,10=4,14=-1,18=1000120,52=2,53=2032/20;
 3/5=7,11=2,16=1,17=8,25=1,30=1,74=-5/1,2,3;
 4//1;
 5/5=2,6=10,38=5,94=2/2;
 8/6=4,10=90,11=11/1;
 11/6=1,8=1,9=11,15=111,16=1,31=1/1,2,10;
 10/6=1,7=6,31=1/2;
 6/7=2,8=2,9=2,10=2,28=1/1;
 7/7=1,10=1,18=20,25=1,30=1,33=-1/1,2,3,16;
 1/6=70,8=5,10=4,14=-1,18=1000120,52=2,53=1022,64=2/20;
 3/5=26,6=2,11=9,16=1,25=1,30=1/1;
 4/20=10,22=2,24=3,28=10/2;
 7/7=1,25=1,30=1,33=-1,44=-1/16;
 1/6=70,8=5,10=4,14=-1,18=1000120,52=2,53=3016,64=2/20;
 7/9=1,25=1,44=-1/16;
 1/6=70,8=5,10=4,14=-1,18=1000020,52=2,64=2/3(1);
 99//99;
 2/9=110,15=1/2;
 1/6=70,8=5,14=-1,18=1000020,52=2,53=3173,64=2/20;
 3/5=26,6=2,11=9,16=1,25=1,30=1/1;
 4/16=2,20=10,22=1,24=3,28=10/2;
 7/7=1,30=1,33=-1,44=-1/16;
 1/6=70,8=5,14=-1,18=1000020,52=2,53=2033/20;
 3/5=7,6=1,11=2,16=1,17=8,25=1,30=1,74=-5,82=7/1,2,3;
 4/5=5,16=3/1;
 5/5=2,6=10,38=5,94=2/2;
 7/7=1,30=1,33=-1/1,2,3,16;
 1/6=70,8=5,14=-1,18=1000020,52=2,53=1023,64=2/20;
 3/5=26,6=2,11=9,16=1,25=1,30=1/1;
 4/16=2,20=10,22=1,24=3,28=10/2;
 7/7=1,30=1,33=-1,44=-1/16;
 1/6=70,8=5,14=-1,18=1000020,52=2,53=3015,64=2/20;
 7/9=1,44=-1/16;
 1/6=70,8=5,14=-1,18=1000020,52=2,64=2/3(-16);
 2/9=110,15=1/2;
 99//99;

Questions regarding the above example

1. IOp(1/14)=-1 -1 is not mentioned as an option in the IOps reference
2. IOp(1/18)=1000120 (Does this mean the sum of three options?)
3. At the end of line 1 there is a "/1,3;" What does this mean?
4. IOp(3/74)=-5 (see line 8) do not exist in the IOps refernence
5. On line 9 one sees "4//1" What does it mean?
6. On some lines there is a number in parenthesis at the end. Could someone explain what this mean?

When a satisfactory explanation has been provided, the above questions could be removed.

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.

Old version of Gaussian, G98

http://aliga.iciq.es/wiki/images/files/g98/index.htm