Using Gaussian98
#b3pw91/6-311g(d) scf=direct fopt
Next to the Lowest Energy Structure

 Optimized Geometry

 0.000000    0.000000    2.878461
 0.000000    0.000000   -2.878461
 0.000000    2.878461    0.000000
-2.878461    0.000000    0.000000
 0.000000   -2.878461    0.000000
 2.878461    0.000000    0.000000


                    Distance matrix (angstroms):
                         1          2          3          4          5
     1  Ca   0.000000
     2  Ca   5.756922   0.000000
     3  Ca   4.070759   4.070759   0.000000
     4  Ca   4.070759   4.070759   4.070759   0.000000
     5  Ca   4.070759   4.070759   5.756922   4.070759   0.000000
     6  Ca   4.070759   4.070759   4.070759   5.756922   4.070759
                    6
     6  Ca   0.000000

 SCF Done:  E(RB+HF-PW91) =  -4065.1368680 au

 E(6 atoms of Calcium) = -4065.058697 au

 Binding Energy = 2.1272 ev (0.3545 ev/atom)