Using Gaussian98
b3pw91/6-311g(d) scf=direct fopt

Optimized Structure

 0.000000    2.776508    1.619772
-1.963288   -1.963288   -1.619772
 2.776508    0.000000    1.619772
-2.776508    0.000000    1.619772
 0.000000   -2.776508    1.619772
 1.963288    1.963288   -1.619772
 1.963288   -1.963288   -1.619772
-1.963288    1.963288   -1.619772

                    Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   6.067521   0.000000
     3  Ca   3.926575   6.067521   0.000000
     4  Ca   3.926575   3.874335   5.553016   0.000000
     5  Ca   5.553016   3.874335   3.926575   3.926575   0.000000
     6  Ca   3.874335   5.553016   3.874335   6.067521   6.067521
     7  Ca   6.067521   3.926575   3.874335   6.067521   3.874335
     8  Ca   3.874335   3.926575   6.067521   3.874335   6.067521
                    6          7          8
     6  Ca   0.000000
     7  Ca   3.926575   0.000000
     8  Ca   3.926575   5.553016   0.000000


SCF Done:  E(RB+HF-PW91) =  -5420.23488095 au

 E(8 atoms of Calcium) = -5420.078262 au

 Binding Energy = 4.26185 ev (0.5327 ev/atom)