Madelung constant check: 1.7475645946331821 (1.747565)

room temperature (Lazarus 1949): a = 5.6402 A, density 2163 kg/m^3; input bulk modulus B = 24.57 GPa
  fitted repulsion: rho = 0.3155 A, lambda = 1266.3 eV; model pressure at a: +0.000 GPa (should be 0)
  elastic constants (GPa)   model: C11 48.33  C12 12.68  C44 12.68   measured: 49.1 12.3 12.8
  [100] L        model    4726 m/s   measured    4764 m/s   ratio 0.992
  [100] T        model    2421 m/s   measured    2432 m/s   ratio 0.995
  [110] L        model    4468 m/s   measured    4484 m/s   ratio 0.996
  [110] T(slow)  model    2870 m/s   measured    2916 m/s   ratio 0.984
  [111] L        model    4379 m/s   measured    4387 m/s   ratio 0.998
  [111] T        model    2729 m/s   measured    2764 m/s   ratio 0.987
  Coulomb forces alone (same spacing, no repulsion): C11 -46.62  C12 12.68  C44 18.00 GPa; pressure -10.62 GPa (inward: the crystal would collapse)

80 K (Rose 1936): a = 5.6 A, density 2210 kg/m^3; input bulk modulus B = 27.00 GPa
  fitted repulsion: rho = 0.2976 A, lambda = 1942.2 eV; model pressure at a: +0.000 GPa (should be 0)
  elastic constants (GPa)   model: C11 54.89  C12 13.05  C44 13.05   measured: 57.6 11.7 13.32
  [100] L        model    4983 m/s   measured    5105 m/s   ratio 0.976
  [100] T        model    2430 m/s   measured    2455 m/s   ratio 0.990
  [110] L        model    4612 m/s   measured    4659 m/s   ratio 0.990
  [110] T(slow)  model    3076 m/s   measured    3222 m/s   ratio 0.955
  [111] L        model    4482 m/s   measured    4500 m/s   ratio 0.996
  [111] T        model    2877 m/s   measured    2988 m/s   ratio 0.963
  Coulomb forces alone (same spacing, no repulsion): C11 -47.97  C12 13.05  C44 18.52 GPa; pressure -10.93 GPa (inward: the crystal would collapse)
