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

Optimized Structure

 3.038433    0.000000    1.821036
-3.078151   -2.095436   -0.008834
 0.824913   -2.884343    0.005069
 0.824913    2.884343    0.005069
 3.052830    0.000000   -1.819719
-0.783038    0.000000   -1.901090
-3.078152    2.095436   -0.008833
-0.801747    0.000000    1.907302

                        Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   6.719514   0.000000
     3  Ca   4.064092   3.982019   0.000000
     4  Ca   4.064092   6.327108   5.768686   0.000000
     5  Ca   3.640784   6.727487   4.075892   4.075893   0.000000
     6  Ca   5.334591   3.638548   3.812923   3.812923   3.836730
     7  Ca   6.719515   4.190872   6.327109   3.982020   6.727488
     8  Ca   3.841149   3.639291   3.818893   3.818894   5.361758
                    6          7          8
     6  Ca   0.000000
     7  Ca   3.638549   0.000000
     8  Ca   3.808438   3.639292   0.000000



SCF Done:  E(RB+HF-PW91) =  -5420.25668629 au

 E(8 atoms of Calcium) = -5420.078262 au

 Binding Energy = 4.8552 ev (0.6069 ev/atom)