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

Optimized Structure

-0.093164   -0.132972   -3.547018
 0.000000    0.000000    0.000000
 2.214393    3.054747   -1.428378
-0.367977   -3.655717   -1.706557
 0.367977    3.655717    1.706557
-2.214393   -3.054747    1.428378
 1.733430   -2.694342    1.530514
-1.733430    2.694342   -1.530514
-3.093265    0.830373    1.534310
 3.341884    1.472682    1.705022
 3.093265   -0.830373   -1.534310
-3.341884   -1.472682   -1.705022
 0.093164    0.132972    3.547018


SCF Done:  E(RB+HF-PW91) =  -8807.98791995 au

E(13 atoms of Calcium) = -8807.627176 au

Binding Energy = 9.81642 ev (0.75511 ev/atom)