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

-1.999432    1.927451   -1.810318
 2.000652    1.810803    1.925757
 1.999533   -1.811940   -1.925713
-2.000728   -1.926314    1.810271
 1.999492   -1.927437    1.810258
-2.000722   -1.810793   -1.925696
-1.999587    1.811928    1.925654
 2.000792    1.926302   -1.810212

                   Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   5.474718   0.000000
     3  Ca   5.476137   5.287540   0.000000
     4  Ca   5.287738   5.476351   5.474737   0.000000
     5  Ca   6.630243   3.740024   3.737756   4.000220   0.000000
     6  Ca   3.740024   6.630282   4.000255   3.737753   5.474731
     7  Ca   3.737758   4.000239   6.630113   3.740022   5.476203
     8  Ca   4.000224   3.737754   3.740026   6.630439   5.287638
                    6          7          8
     6  Ca   0.000000
     7  Ca   5.287439   0.000000
     8  Ca   5.476435   5.474743   0.000000

    SCF Done:  E(RB+HF-PW91) =  -5420.19304190

 E(8 atoms of Calcium) = -5420.078262 au

  Binding Energy = 3.12334 ev (0.3904 ev/atom)