Subject: CCL:Re: ab-initio and TM's

From: Seiji Mori(nakamura lab) <[email-masked]>
Date: Sat, 8 Jul 95 12:50:01 JST

J. Pollard wrote:
>I was wondering if get peoples opinion on the best (or most accepted)
>method to perform ab-initio calculations with second and third row TM
>complexes.  I am familiar with all the semi-empirical approaches but am
>not with any ab-initio.  What basis sets work best?  Relativistic effects?
>Thank you and I look forward to responses.   J. Pollard

Dear Pollard;

 I am investigating the reaction pathway in the reaction with organometallics
 with ab initio method. As you  know, recently, Semiemperical MNDO/d and PM3(tm)
hamiltonian is work well in the TM complex, for example Cr,Pt(II), Fe and so on.
 Basically, Pople and Hehre's 3-21G and 6-31G* basis sets( combined Hartree-Fock

theory) provide good results
 for main group element
 such as C,H,N,O,Cl,Li,Mg.....
 I devided the section ,first row transition metals , heavier transition metals:
 (1) First-row transiiton metals:
  3-21G basis set is also avalable for Sc-Zn ,  however, especially in the first
 transition metals, the description of d orbital(3d) is cheep because 3d  
fitting
 by Gaussian-type function as compared to Slater type function is difficult.
 So, we use the rich basis sets contained basis functions,
 for example,
 Wachters basis set with Hay's d function :Wachters, et al.JCP, 1970, 52,1033.
 Hay, JCP, 66,4377(1977)
 The problem of these basis sets is very huge, so the costs of computation is
 higher than 3-21G basis set .Number of basis functions of Zn (for example)
 is 27 at the 3-21G basis set
 and 39 the Wachters+Hay basis set . As to calculation of Zn atom,computer time
 is 42.1 sec by Gaussian94 in my Workstation in former,53.3sec in latter.
 Then we also use the effctive core potential method(ECP), that is, the core 
orbital
 is fitting by potential function, the valence orbital are used basis functions.
 The most famous ECP is editted by Hay&Wadt,Hay and Wadt,JCP,82,270,299(1982)
These functions are relavistic ECP.
  In the Moller-Plesset perturbation theory combined with these basis set
 ,whether you use all electron basis sets or basis sets including ECP, the
 result is good agreement with the experiment ,In the Hartree-Fock method, the
results sometimes are poorer than MP2 theory. In the Fe,Ni compunds (the system
including the elements we have to
take high-spin state into account),even if we use MP2 theory, the results are
sometimes poor.Higher-cost CI(configration-interaction) method may be better.
  
As to the structual reliability  of
methylmetalchloride(M= Ti, Ge,Sn,Pb) compounds , you can see:
G. Frenking, Marburg, reported  in J. Comp.Chem.13,919,935(1992).

 (2) Heavier transition metals
And The element bigger than 4-th row element, the relavistic effect is affected
 to the chemical behaviors.We use ECP such as Hay&Wadt ECP because in the ECP me
thod,
we can take the relavistic effect into account.
 Recently, Stevens also reported the relavistic ECP in Can.J.Chem. 70,612(1992) 
(K-La,Hf-Rn) or JCP, 98, 5555(1993)(Ce-Lu) about from third-row to
Lanthanide elements, however, I don't know papers about the reliability of Stevens ECP.

  Sincerely yours:

 Seiji Mori
 Department of Chemistry
 The University of Tokyo
 email:[email-masked]