fig5

Figure 5. (A) Average potential energies of the Invar (top lines), fcc Fe (bottom lines), and fcc Ni (bottom, green dotted line) as a function of the first NN distance at T = 0. For Fe, two types of the potentials for the HS (red solid line) and LS (blue dashed line) states are depicted. (B, C) Simulated first NN interatomic distance around Fe (B) and Ni (C) given by the PIECP (blue circles and solid line, quantum) and the classical MC (green diamond and dashed line, classic) methods, together with the experimental EXAFS data (red open circle with an error bar). (D) Equilibrium first NN distance (a₀/√2) given by the PIECP and classical MC simulations, together with the experimental literature data^[44].