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

 3.700281    0.001682   -0.000109
 0.001693   -3.700257    0.000986
-3.700261   -0.001718    0.000103
-0.000113   -0.000991   -3.700262
-0.001707    3.700283   -0.000992
 0.000098    0.000987    3.700269
 0.000009    0.000014    0.000005

                    Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   5.232963   0.000000
     3  Ca   7.400543   5.232939   0.000000
     4  Ca   5.232978   5.232954   5.232953   0.000000
     5  Ca   5.233008   7.400541   5.232983   5.232976   0.000000
     6  Ca   5.232987   5.232963   5.232963   7.400532   5.232985
     7  Ca   3.700272   3.700271   3.700271   3.700267   3.700270
                    6          7
     6  Ca   0.000000
     7  Ca   3.700265   0.000000


E(RB+HF-PW91) =  -4742.64375180

 E(7 atoms of Calcium) = -4742.568480 au

  Binding Energy = 2.0483 ev (0.2926 ev/atom)