Subject: ab initio hyperfine constants

From: "Adrian Radomir Jaszewski" <[email-masked]>
Date: Fri, 5 May 2000 20:20:50 MET

Dear CCL'ers,

I have read some papers of Chipman, Feller and Carmichael
about evaluation of the isotropic hyperfine coupling
constants (HFCC's) from ab initio methods. Unfortunately,
I have got some problems in the application (Gaussian94/98)
of the procedures described there, that are mainly of 
technical nature. 
Let me use the computations of the isotropic splittings for
NO radical (2 PI) as an example [D.Feller et al. J.Chem.Phys.
99 (1993) 2829].

Determination of the isotropic hyperfine constants using 
a given method (QCISD for instance), that are listed as 
a part of the population analysis output, requires inclusion
of the keyword Density=Current in the job's route section:
  
%chk=filename
# UQCISD=(Conver=8,Full)/Gen SCF=(Tight,NoDIIS,MaxCyc=256)
# Density=Current Prop=EPR

Title section

0   2
o    0.000000    0.000000    0.000000
n    1.150431    0.000000    0.000000

basis set description

Of course, SCF and Prop=EPR keywords denote single point 
(but with tight convergence criteria) calculations and 
evaluation of the anisotropic hyperfine couplings, respectively.
The main problem is that the generalized densities are 
available only for HF, MP2, MP3, MP4(SDQ), QCISD, CCD and CISD
methods.

MY QUESTIONS ARE:
1. How to calculate HFCC's using CCSD method that are included 
in Table II of the originally paper?
2. How to calculate HFCC's using QCISD(T) method? One can do this
from spin densities derived by finite-field perturbation theory 
in the presence of small Fermi contact field at each nucleus 
in turn but what changes in the input file should be made (in
comparison with this listed above). Should I use 
the Field=F(AtomNumber)FileSize command?
3. How to calculate HFCC's using CCSD(T) method?
4. How to calculate HFCC's using QCISD(TQ) method? Perturbation 
theory approach allows the inclusion of the effect of quadruple 
replacement through fifth order but how to avoid Density keyword
restrictions and what commands should be added to the route section
of the input file?
5. How to calculate spin polarization contribution using 
ROHF-SCI method and how to obtain core and valence components
of the polarization terms? Direct contribution to HFFC's can
be obtained from ROHF wave function. The simplest way to 
incorporate spin polarization effects is to make the UHF 
computations but UHF wave function tends to significantly
overestimate these contributions. The effect of spin polarization
can be evaluated from ROHF-SCI wave function but RO is available
only for HF and DFT energies and gradients and MP2 energies.
Thus what commands should be added to the input file to avoid 
this restriction and allow to calculate ROHF-SCI HFCC's?
If it is possible, FrozenCore and Full calculations should thus 
give me a core-valence analysis, I suppose.
 
I hope that CCL will prove once again that is very effective in 
filling the gaps of my porous personal knowledge.

Thank you in advance.
I will summarize.

Adrian

===============================================
Adrian R. Jaszewski
Faculty of Chemistry
UNIVERSITY OF WROCLAW
14 Joliot-Curie St.
50-383 Wroclaw
Poland
e-mail: [email-masked]
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