density functional question

[CUNDARIT%MEMSTVX1.BITNET "-at-" OHSTVMA.ACS.OHIO-STATE.EDU]

 Hi,
         Our group has just started experimenting with LDF in a small way
 for transition metal calcs.  We are trying to calculate the binding energy
 of H2 to Cr(CO)5, in conjunction with some work by Ted Burkey in our Dept.
 who has made the first exptl. determination of this quantity.  Given our
 lack of experience with LDF we want to be sure we are not making any
 serious mistakes. We are using DMol at the San Diego Supercomputer Center.
         First question: Are LDF methods size-consistent?
         Second question: Does anybody have any feeling for the effect of
 freezing the core density in such calcs. on properties such as energetics
 and geometry?
         Third question: I have just calcd. a binding energy of -30 kcal/mol
 from E(Cr(CO)5(H2)) - E(Cr(CO)5) -E(H2) using the equivalent of a double-zeta-
 valence-plus-polarization basis set, and a FINE mesh size.  Should I believe
 this or is it worth the expense to go to a larger basis set, finer mesh,
 unfrozen core?
         All suggestions are welcome.
                                         Tom Cundari, Asst. Prof.
                                         Dept. of Chemistry
                                         Memphis State University
                                         Memphis, TN 38152
                                         phone:901-678-2629
                                         fax:901-678-3447
                                         e-mail:cundarit "-at-"
 memstvx1.memst.edu