I am calculating the heats of reactions containing
organo-mercury compounds. I am using G03 and DFT methods. The program, when
mercury is involved, defaults to an unpruned integration grid for this atom.
The manual states that one should use the same grid when comparing energies.
Does this mean that I should be defining an unpruned grid for all of my
calculations i.e. the compounds without mercury in the isodesmic reaction? If
so how do I define an unpruned grid the same as the one being used by gaussian
when mercury is involved. The manual does not talk about unpruned grids. I have
enclosed the relevant output section below.
Only the mercury atom will use
the unpruned grid. All the
atoms will use
the default, pruned grid if it is defined.
So you need not do anything
special in generating the pieces of
reaction. Each element will be
done the same way if you use
the defaults in
The point of printing the
informational message is in the event that
you compare with
another program or a future release of Gaussian were
a pruned grid
for mercury might be used.
I think the
manual is referring to using different grid densities, that
INT=ULTRAFINE versus INT=FINE. A pruned grid has some of the
the word 'pruned') so it is faster, but it should give
the same result
as an unpruned grid, for the same integration grid
To summarise, I
think you don't need to worry about the pruned grid, so
long as you use
the same integration grid density (for example, the
integration grid density) for all calculations.
Ian Hovell -
Centro de Tecnologia Mineral - CETEM
Ministerio da Ciência e da Tecnologia- MCT
Avenida Ipê, No 900 - Cidade Universitaria
Ilha do Fundão Rio de Janeiro RJ Brasil
tel 00 55 (xx) 3865 7344 ou 3865 - 7216
Fax 00 55 (xx) 22602837 ou 2290-4286