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

Optimized Structure

-3.406950    1.130523    1.238831
 1.968221   -2.594381    1.320368
-0.002873   -3.009177   -1.990638
 2.060701    2.365856   -2.051260
-0.000089    0.009695   -0.263725
 3.407851    1.122044    1.242502
 3.713355   -1.159603   -1.588198
-3.713291   -1.151303   -1.591770
-0.002507    0.196872    3.379396
 0.003681    3.309800    1.040234
-2.049191    2.370071   -2.054683
-1.978909   -2.590397    1.318944

                    Distance matrix (angstroms):
                    1          2          3          4          5
     1  Ca   0.000000
     2  Ca   6.540185   0.000000
     3  Ca   6.257342   3.875568   0.000000
     4  Ca   6.499689   5.998365   5.757864   0.000000
     5  Ca   3.888526   3.628334   3.477906   3.604668   0.000000
     6  Ca   6.814808   3.986278   6.257253   3.769714   3.888457
     7  Ca   7.995969   3.682911   4.170519   3.921040   4.112317
     8  Ca   3.648681   6.545426   4.168693   6.776469   4.110899
     9  Ca   4.128433   3.989293   6.254280   6.201075   3.647927
    10  Ca   4.052295   6.228744   7.008260   3.831409   3.548382
    11  Ca   3.771900   7.223320   5.755679   4.109896   3.602461
    12  Ca   3.986348   3.947132   3.877297   7.227806   3.630572
                    6          7          8          9         10
     6  Ca   0.000000
     7  Ca   3.648576   0.000000
     8  Ca   7.994490   7.426652   0.000000
     9  Ca   4.129504   6.350168   6.348227   0.000000
    10  Ca   4.051613   6.375414   6.375325   3.893846   0.000000
    11  Ca   6.496792   6.773710   3.922193   6.200074   3.830912
    12  Ca   6.542572   6.549849   3.681213   3.990050   6.230624
                   11         12
    11  Ca   0.000000
    12  Ca   5.999379   0.000000

SCF Done:  E(RB+HF-PW91) =  -8130.44480270 au

E(12 atoms of Calcium) = -8130.117394 au

Binding Energy = 8.90931 ev (0.74244 ev/atom)