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


Optimized Structure

 0.000000    2.993830    0.000000
 2.993830    0.000000    0.000000
 0.000000   -2.993830    0.000000
-2.993830    0.000000    0.000000


                    Distance matrix (angstroms):
                    1          2          3          4
     1  Ca   0.000000
     2  Ca   4.233915   0.000000
     3  Ca   5.987660   4.233915   0.000000
     4  Ca   4.233915   5.987660   4.233915   0.000000

 SCF Done:  E(RB+HF-PW91) =  -2710.06146705

 E(4 atoms of Calcium) = -2710.039131 au

 Binding Energy = 0.6078 ev (0.1519 ev/atom)