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


Optimized Structure

 1.331761    1.331761    1.331761
-1.331761   -1.331761    1.331761
-1.331761    1.331761   -1.331761
 1.331761   -1.331761   -1.331761

                    Distance matrix (angstroms):
                     1          2          3          4
     1  Ca   0.000000
     2  Ca   3.766789   0.000000
     3  Ca   3.766789   3.766789   0.000000
     4  Ca   3.766789   3.766789   3.766789   0.000000

 SCF Done:  E(RB+HF-PW91) =  -2710.10436675 au

 E(4 atoms of Calcium) = -2710.039131 au

 Binding Energy = 1.7751 ev (0.4438 ev/atom)
 
Single Point Energy Calculation
b3pw91/6-311+g(df)
2 hours 1 minute
-2710.10481259 Hartrees
B.E. 0.446028 ev/atom