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

-1.569830    1.724574   -1.209093
 2.276895    0.497686   -1.210917
-0.708303   -2.222558   -1.208235
-3.728530   -0.814105    0.655720
 1.159290    3.635018    0.656745
 2.570385   -2.820429    0.656175
 0.000093   -0.000186    1.659605

                    Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   4.037642   0.000000
     3  Ca   4.040060   4.038705   0.000000
     4  Ca   3.818692   6.424194   3.818356   0.000000
     5  Ca   3.818278   3.818384   6.424738   6.609500   0.000000
     6  Ca   6.424770   3.818646   3.818805   6.610724   6.607874
     7  Ca   3.697146   3.697512   3.696657   3.946250   3.945145
                    6          7
     6  Ca   0.000000
     7  Ca   3.945509   0.000000


     E(RB+HF-PW91) =  -4742.70922762

 E(7 atoms of Calcium) = -4742.568480 au

 Binding Energy = 3.82997 ev (0.5471 ev/atom)