Re: CCL:Atomic charges: Ni, Co

Petr Toman wrote:
 >
 > Dear CCLers,
 > I wonder if there is a suitable method for calculation of atomic charges
 > in molecules containing Ni or Co.
 > I tried Pop=MK in Gaussian 98, but...
 >  Merz-Kollman atomic radii used.
 >  GetVDW:  no radius for atom   1 atomic number  28.
 This seems to be related to a recent question about the same topic.
 >From my own experience, best results for partial charges are obtained
 by:
 a. Using the set sampling points of Breneman & Wiberg (the 'ChelpG'
 keyword).
 b. Restricting the dipole moment (the 'Dipole' keyword).
 The command line then reads something like:
 # HF/6-31G** Pop=(ChelpG,Dipole) etc.
 The reference to the Breneman & Wiberg paper is:
 Breneman, C.M. & K.B. Wiberg (1990). J. Comp. Chem. 11, 361-373.
 ChelpG is the only method which uses a lot of sampling points, and it
 can cope with additional charge centres (MK can't in my experience,
 Gaussian crashes).
 Restricting the dipole moment has two advantages:
 a. At long distances, the monopole of a neutral molecule is neglegible
 (=zero), and the dipole interactions are next in importance.
 b. There are quite a lot of degrees of freedom, which can render some
 pairs of atoms ill-defined (dependent on each other). Restricting the
 dipole moment might not solve this problem completely, but at least will
 push the calculation in the right direction.
 If anyone can think of a disadvantage, I'd like to know.
 If the molecule contains atoms for which Gaussian has no atomic radius
 available, you must split your job (otherwise Gaussian crashes):
 1. Run the optimisation / single point job, specifying a checkpoint
 file.
 2. Run the ESP job.
 The command line for the second step reads:
 # HF/6-31G** Pop=(ChelpG,Dipole,ReadRadii) Density=CHK Geom=checkpoint
 etc.
 This indicates that both the electron density and the molecular geometry
 must be read from the checkpoint file.
 The 'ReadRadii' keyword indicates that at the end of the input radii for
 the ChelpG calculation are provided. The format of the radii is:
 Blank line
 'Atomic number' 'radius in Angstrom'
 Blank line
 Blank line
 So for the calculation of the a molecule containing bromine, after
 having run the single point calculation, the entire input file is as
 simple as:
 *****************************************
 $ RunGauss
 %Chk=C14H28Br2.chk
 # HF/6-31G** Pop=(ChelpG,Dipole,ReadRadii) Density=CHK SCF=Direct
 Geom=(checkpoint,NoDistance,NoAngle)
 1,14-dibromotetradecane
 0 1
  35 1.85
 *****************************************
 I hope it is clear that your optimisation / single point job must
 contain '%Chk=C14H28Br2.chk' as its second line.
 Comments and experiences welcomed.
 Hope this helps,
 --
 Jacco van de Streek (mailto:jaccos $#at#$ sci.kun.nl)
 Dept. of Solid State Chemistry
 University of Nijmegen
 The Netherlands