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


Optimized Structure

 0.000000    1.888150    0.000000
 0.000000   -1.888150    0.000000
 0.000000    0.000000    3.572305
 0.000000    0.000000   -3.572305

                    Distance matrix (angstroms):
                    1          2          3          4
     1  Ca   0.000000
     2  Ca   3.776300   0.000000
     3  Ca   4.040603   4.040603   0.000000
     4  Ca   4.040603   4.040603   7.144610   0.000000

 SCF Done:  E(RB+HF-PW91) =  -2710.07694181

 E(4 atoms of Calcium) = -2710.039131 au

 Binding Energy = 1.0289 ev (0.2572 ev/atom)