Using binary Morse potential model V(r) = D0 * ( exp(2 * BETA * (R0-r)) - 2 * exp(BETA * (R0-r)) ), and cutoff scheme W(r) = V(r) - V(RC) - V'(RC) * (r - RC), we arrive at optimized parameter set (upper_bound fitted lower_bound): [2] A_ZrC[A^-1] B_ZrC[A] 6.00000000000000 4.50000000000000 3.24594393670078 2.05680151419138 1.00000000000000 1.00000000000000 [2] C_ZrC[A^-1] D_ZrC[A] 3.00000000000000 4.50000000000000 0.82303818052368 4.15482225815134 0.80000000000000 1.00000000000000 [2] ALPHA_ZrC BETA_ZrC 3.00000000000000 20.00000000000000 1.80851303846160 14.59347394373564 1.00000000010000 1.00000000000000 At 0K in equilibrium, the current model predicts NaCl lattice constant = 4.692057 [4.695000] A (-0.06%) -> density = 6.638136 [6.625660] g/cm^3 (0.19%) cohesive energy = 15.996943 [15.840000] eV/unit cell (0.99%); ZnS lattice constant = 5.058610 [5.060234] A (-0.03%) -> density = 5.297153 [5.292053] g/cm^3 (0.10%) cohesive energy = 15.008316 [14.714503] eV/unit cell (2.00%); CsCl lattice constant = 2.962080 [2.914533] A (1.63%) -> density = 6.596078 [6.924194] g/cm^3 (-4.74%) cohesive energy = 12.812194 [13.347951] eV/unit cell (-4.01%); ZnS/NaCl separation = 0.988627 [1.125497] eV (-12.16%); CsCl/ZnS separation = 2.196122 [1.366552] eV (60.71%); Bulk modulus = 207.726921 [227.933333] GPa (-8.87%); C11 = 381.143844 [480.200000] GPa (-20.63%); C12 = 121.018459 [101.800000] GPa (18.88%); C44 = 177.692221 [169.700000] GPa (4.71%); Schottky energy = 5.378139 [8.942340] eV (-39.86%); hcp Zr lattice constant = 3.193818 A; Zr atomic volume = 22.991398 [23.200000] A^3 (-0.90%); Zr bulk modulus = 102.378285 [96.800000] GPa (5.76%); hcp Zr cohesive energy = 6.092416 [6.270000] eV/atom (-2.83%); fcc C lattice constant = 0.000000 A; C atomic volume = 0.000000 [8.800000] A^3 (-100.00%); C bulk modulus = inf [33.000000] GPa (inf%); fcc C cohesive energy = 7.430000 [7.430000] eV/atom (0.00%); ZrC heat of formation = 2.474527 [2.140000] eV/pair (15.63%); In configuration "ZrC_CDIS" (lattice constant [A] = 4.692057), the atomic coordinates and force constants [N/m] are Zr: s= 0.00 0.00 0.00, fx= -69.85851 [-48.40000] ( 44.34%); Zr: s= 0.00 0.50 0.50, fx= 4.46659 [-9.17000] (-148.71%); Zr: s= 0.50 0.00 0.50, fx= -45.20301 [-47.64000] ( -5.12%); Zr: s= 0.50 0.50 0.00, fx= -45.20301 [-47.64000] ( -5.12%); C: s= 0.50 0.50 0.50, fx= 0.06097 [ 1.56000] ( -96.09%); C: s= 0.49 0.00 0.00, fx= 203.17589 [199.43000] ( 1.88%); C: s= 0.00 0.50 0.00, fx= -23.71946 [-24.07000] ( -1.46%); C: s= 0.00 0.00 0.50, fx= -23.71946 [-24.07000] ( -1.46%); In configuration "ZrC_ZrDIS" (lattice constant [A] = 4.692057), the atomic coordinates and force constants [N/m] are C: s= 0.00 0.00 0.00, fx= -69.89873 [-48.40000] ( 44.42%); C: s= 0.00 0.50 0.50, fx= 4.46691 [-9.17000] (-148.71%); C: s= 0.50 0.00 0.50, fx= -45.20790 [-47.64000] ( -5.11%); C: s= 0.50 0.50 0.00, fx= -45.20790 [-47.64000] ( -5.11%); Zr: s= 0.50 0.50 0.50, fx= 6.43395 [-8.69000] (-174.04%); Zr: s= 0.49 0.00 0.00, fx= 282.20632 [274.84000] ( 2.68%); Zr: s= 0.00 0.50 0.00, fx= -66.39632 [-56.65000] ( 17.20%); Zr: s= 0.00 0.00 0.50, fx= -66.39632 [-56.65000] ( 17.20%); step 248: error = 0.013104 Saving atomic configuration in "NaCl". Saving atomic configuration in "ZnS". Saving atomic configuration in "CsCl". Saving atomic configuration in "ZrVAC". Saving atomic configuration in "CVAC". Saving atomic configuration in "PureZr". Saving atomic configuration in "PureC". Saving atomic configuration in "ZrC_CDIS". Saving atomic configuration in "ZrC_ZrDIS". Saving atomic configuration in "ZrC_TEST". Plotting cohesive energy curves in "coh.m".