Editing G03

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'''You MUST use the "p" keyword''' for extra-print in '''all your calculations'''. 

This is an essential requirement to use afterwards the Chemical Repository, where you will need to save your data.


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==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 questions & answers ==
[[Issues related to the output ]]

== Links ==

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

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

Introduction and input/output explanation of PCM
 
http://www.cup.uni-muenchen.de/oc/zipse/compchem/solv/pcm.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, BONDI.. which consider hydrogens explicitly.

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

* Often Gaussian has problems computing the cavity in specific structures, giving an error message like the one below...

AdVTs1: ISph= 3760 is engulfed by JSph= 3762 but Ae( 3760) is not yet zero!

There are two methods to solve this:

-1- Increase the RMIN value used in the calculation.
Increasing the RMIN value smooths the surface of the spheres that make the cavity and helps prevent overlapping.
The default value in Gaussian 03 is RMIN=0.20, but you can use any value up to 0.40. You should try to keep the new RMIN within 0.1 vs the default, as a larger difference will give errors in the solvation free energy to the 4th decimal place (from 0.05 kcal/mol upwards).

-2- 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.