EH parameters for solids

[<ABULJAN%UCANORTE.BITNET \\at// phem3.acs.ohio-state.edu>]

 Dear Netters!
             Presently, we are attempting to determine the
 electronic structure (band structure, DOS, COOP, etc) of
 solid state compounds syntetized and characterized in our
 laboratory (MCuFeX2, M=Li,Na,K,Cs,Rb and X=S,Se,Te) using
 extended Huckel tight-binding method (EHMACC package)
            However, we have several doubts about the way
 of choosing orbital parameters (Hii, Slater exponents).
 We has nearly reproduced the band structure of (Mn2P2)-2
 determined by Dr. R. Hoffmann ("Solids and Surfaces,
 R. Hoffmann, VCH Publishers, 1988, p.60), using the
 orbital parameters of Mn given in the Alvarez's Tables:
     Hss = -7.5      exp s = 1.80
     Hpp = -3.8      exp p = 1.80
     Hdd = -8.7      exp d1 = 5.15    c1 = 0.514
                     exp d2 = 1.70    c2 = 0.693
         However, we attempted to improve our results using
 the orbital parameters given by Kematics and Myers for the
 Mn in a MnAl alloy (Inorg.Chem, (1992), p.3568-3572), but
 the band structure obtained has no similarity with the
 Hoffmann's band structure for the (Mn2P2)-2.
        Our question  are the following:
 -What are the criteria for choosing the orbital parameters
 for elements in a EH-tight-binding calculation?
        If someone have any insinuation or comments about
 possible orbital parameters for our solid state compounds,
 you are welcome to give us.
       A last thing. I'm intrigued because this list are
 dominated by the molecular quantum chemist and almost no
 posting about solid state quantum chemistry.
      In advence, I appreciate and thank for your comments
 and helps.
             ANTONIO BULJAN H
             Dept. of Chemistry
             Universidad Catolica del Norte
             abuljan \\at// ucanorte.bitnet
             abuljan \\at// socompa.cecun.ucn.cl