The EXP pair-potential system. III. Thermodynamic phase diagram

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This paper determines the thermodynamic phase diagram of the EXP system of particles interacting by the purely repulsive exponential pair
potential. The solid phase is face-centered cubic (fcc) at low densities and pressures. At higher densities and pressures, the solid phase is bodycentered cubic (bcc) with a re-entrant liquid phase at the highest pressures simulated. The investigation first identifies the phase diagram at
zero temperature at which the following four crystal structures are considered: fcc, bcc, hexagonal close packed, and cubic diamond. There is a
T = 0 phase transition at pressure 2.651 × 10−3 with the thermodynamically stable structure being fcc below and bcc above this pressure. The
densities of the two crystal structures at the phase transition are 1.7469 × 10−2
(fcc) and 1.7471 × 10−2
(bcc). At finite temperatures, the fcc–
bcc, fcc-liquid, and bcc-liquid coexistence lines are determined by numerical integration of the Clausius–Clapeyron equation and validated
by interface-pinning simulations at selected state points. The bcc-fcc phase transition is a weak first-order transition. The liquid-fcc–bcc triple
point, which is determined by the interface-pinning method, has temperature 5.9 × 10−5
and pressure 2.5 × 10−6
; the triple-point densities
are 1.556 × 10−3
(liquid), 1.583 × 10−3
(bcc), and 1.587 × 10−3
TidsskriftJournal of Chemical Physics
Udgave nummer150
Antal sider9
StatusUdgivet - 3 maj 2019

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