The importance of accurate interaction potentials in the melting of argon nanoclusters

Abstract

ABSTRACT:The melting temperatures of argon clusters Ar N (N = 13, 55, 147, 309, 561, and 923) and of bulk argon have been obtained from exchange Monte Carlo simulations and are compared using different two-body interaction potentials, namely the standard Lennard-Jones (LJ), Aziz and extended Lennard-Jones (ELJ) potentials. The latter potential has many advantages: while maintaining the computational efficiency of the commonly used LJ potential, it is as accurate as the Aziz potential but the computer time scales more favorably with increasing cluster size. By applying the ELJ form and extrapolating the cluster data to the infinite system, we are able to extract the melting point of argon already in good agreement with experimental measurements. By considering the additional Axilrod-Teller three-body contribution as well, we calculate a melting temperature of T ELJ melt = 84.7 K compared to the experimental value of T exp melt = 83.85 K, whereas the LJ potential underestimates the melting point by more than 7 K. Thus melting temperatures within 1 K accuracy are now feasible.

Equation of state for solid neon from quantum theory

“…We mention that we demonstrated recently that such an approach also leads to very accurate melting temperatures for neon and argon under normal conditions. 47,48 On the experimental side, the measurements presented by different research groups can deviate significantly ͑e.g., see the scatter of data in Fig. 3͒, and more accurate low-and high-pressure measurements for solid neon are required.…”

Finite-temperature quantum simulations of mixed rare gas clusters

“…4,5,18 Although their presence has been known for a long time ͓e.g., the Axilrod-Teller term has been discussed in 1943 ͑Ref. 19͔͒, explicitly calculating them is computationally very demanding and has only become possible in the past few years.…”

“…18,20,21 Recent work has investigated the effect of three-body interactions on melting points and specific heats for argon clusters. 4,5 It was found that the maximum of the heat capacity for Ar 147 shifts down from 50 to 46 K if three-body interactions are taken into account. This amounts to an effect of Ϸ10%.…”

“…3 The necessary corrections appeared larger for Kr-and Xe-containing systems but relatively small for Ar-containing clusters. More recently, melting temperatures for neon and argon clusters containing up to N = 923 atoms have been determined 4,5 using a range of potential energy functions, including conventional and extended Lennard-Jones potentials, interaction potentials including three-body terms, and potentials derived from experimental data. 6,7 The latter have been determined from fits to a range of experimental and theoretical data, including measured second virial coefficients, transport properties, spectroscopic data, and calculated C 6 , C 8 , and C 10 coefficients.…”

“…The Monte Carlo ͑MC͒ simulations with different potentials showed that using accurate representations of the intermolecular interactions provides melting temperatures T m for N → ϱ in close agreement with bulk measurements, whereas T m from simulations with conventional Lennard-Jones potentials were too low compared to experiment. 4,5 Also accurate interaction potentials and Lennard-Jones potentials have been used to investigate and compare the minimum energy structures of argon clusters up to Ar 55 . 8 Here, the only difference found was for the structure of Ar 21 .…”