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

Optimized Structure

 0.000000    0.000000    4.201680
 0.000000    0.000000    0.000000
 0.000000    0.000000   -4.201680

                    Distance matrix (angstroms):
                    1          2          3
     1  Ca   0.000000
     2  Ca   4.201680   0.000000
     3  Ca   8.403361   4.201680   0.000000


 SCF Done:  E(RB+HF-PW91) = -2032.54195128

 E(3 atoms of Calcium) = -2032.529348

 Binding Energy = 0.3429 ev (0.1143 ev/atom)