Subject: SUMMARY: ab initio hyperfine constants

From: "Adrian Radomir Jaszewski" <[email-masked]>
Date: Mon, 22 May 2000 12:56:08 MET

22 May 2000
SUMMARY of the answers to 
AB INITIO HYPERFINE CONSTANTS question

Dear CCL'ers,

I asked a question about the hyperfine constants from 
ab initio methods (listed at the end of this message)
two weeks ago. Thanks a lot to Dr. David Feller. You 
are the only person who has replied. I appreciate 
your efforts highly. 

Many people asked me to summarize the replies in return.
Hence I present this summary compiled from two
letters  from AUTHOR of the paper cited in my  question.  

Good luck with your calculations.
Adrian

------------------------EXCERPTS:--------------------------

I think there may be a misunderstanding here.  In our JCP 
paper on NO we used a finite field approach to computing 
the isotropic hyperfine properties with methods like UMP2, 
UMP3, UMP4 and UQCISD(T). The spin denisty matrix wasn't 
involved.  As far as I know, it isn't possible to obtain 
a UQCISD(T) density matrix from Gaussian. But maybe that 
has changed.

The Gaussian options that we used are as follows:
# UQCISD(T)=FULL/GEN SCF=(DIRECT,NOSINGLEPOINT) 
# UNITS=AU FIELD=F(2)-4

I don't have access to that paper from home (where I'm 
writing this), but I believe we did 2 point differencing 
to predict the isotropic hyperfine property at each nucleus.  
In our procedure, the isotropic hyperfine property is given 
as the derivative of the energy with respect to the applied 
field, evaluated at zero field.  For example, we ran 
calculations at +/- 0.0001 or +/-0.0004 andused a 2-point 
formula to obtain the derivative at zero field.
(f+) - (f-)/2*delta, where f+ is the energy with the positive 
field and f- is the energy at negative field.  Delta is 
the field strength. That just gives you the raw value of 
the property in atomic units.  You then need to convert that 
raw value into something useful, like MHz or G.

This has to be done for each nucleus of interest.

You should be sure to correlate *ALL* electrons, 
as the property is very sensistive to core correlation.  
The other methods require nothing more than changing 
the method indicated in the options.

David Feller                                | [email-masked] 
Environmental Molecular Sciences Lab., K8-91| Box 999
Pacific Northwest National Laboratory       | Richland, WA 99352 
                                            | Fax: 509-375-6631

----------------------MY QUESTION---------------------------
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 
i.e.:  
%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 question 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?