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

Optimized Structure

 1.399746    0.504990    0.000000
-0.435234   -2.258189    1.875395
-0.435234   -2.258189   -1.875395
-2.415076    0.653919    0.000000
-0.435234    3.215844   -1.918708
-0.435234    3.215844    1.918708
 2.756268   -3.074220    0.000000


                    Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   3.810435   0.000000
     3  Ca   3.810435   3.750790   0.000000
     4  Ca   3.817728   3.989644   3.989644   0.000000
     5  Ca   3.794380   6.660350   5.474204   3.763599   0.000000
     6  Ca   3.794380   5.474204   6.660350   3.763599   3.837416
     7  Ca   3.827649   3.790607   3.790607   6.375094   7.309722
                    6          7
     6  Ca   0.000000
     7  Ca   7.309722   0.000000

 SCF Done:  E(RB+HF-PW91) =  -4742.70959380 au

 E(7 atoms of Calcium) = -4742.568480 au

 Binding Energy = 3.8399 ev (0.54856 ev/atom)