Monte Carlo simulation of liquid nalkanes. I

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(Received 2 April 1991; accepted 1 November 1991). The conformational properties of liquid n-alkanes (ranging from n-pentane to n-decane) have.
Monte Carlo simulation of liquid nalkanes. I. Intramolecular structure and thermodynamics N. G. Almarza, E. Enciso, and F. J. Bermejo Citation: The Journal of Chemical Physics 96, 4625 (1992); doi: 10.1063/1.462798 View online: http://dx.doi.org/10.1063/1.462798 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/96/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Phase behavior of n-alkanes in supercritical solution: A Monte Carlo study J. Chem. Phys. 121, 2169 (2004); 10.1063/1.1765103 A Monte Carlo study of the pattern formation during transitions in n-alkane crystals J. Chem. Phys. 112, 7627 (2000); 10.1063/1.481357 Computer simulations of vapor–liquid phase equilibria of nalkanes J. Chem. Phys. 102, 2126 (1995); 10.1063/1.469563 Solubility and thermodynamics of solution of xenon in liquid nalkanes J. Chem. Phys. 80, 4438 (1984); 10.1063/1.447224 Solubility of xenon in liquid nalkanes: Temperature dependence and thermodynamic functions J. Chem. Phys. 77, 3221 (1982); 10.1063/1.444197

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Monte Carlo simulation of liquid n-alkanes. I. Intramolecular structure and thermodynamics N. G. Almarza and E. Enciso Departamento de Qllimica Ftsica, Facllitad de Ciencias Qllimicas, Universidad Compilltense, E-28040 Madrid, Spain

F. J. Bermejo Instituto de E~tructura de fa Materia, C S. l C, Serrano 119, E-28oo6 Madrid, Spain

(Received 2 April 1991; accepted 1 November 1991) The conformational properties of liquid n-alkanes (ranging from n-pentane to n-decane) have been investigated using Monte Carlo computer simulation techniques. The method of simulation combines the "reptation" method with a scheme of preferential sampling, which leads to an improvement of the simulation efficiency. The change of internal properties and structure as an effect of the density is studied.

I. INTRODUCTION

The study ofliquids composed by flexible molecules has attracted great research effort in recent years. 1-16 The influence of temperature and density on the conformation of these systems is one of the more interesting topics in this field. The attainment of accurate descriptions of the solvent effects in the intramolecular structure of these systems by compnter simulation l5 becomes very often a difficult task due to the existence of high barriers in the torsional terms of the intramolecular potential energy. On the other hand, the high density regime also contributes to hinder the attainment of good statistics when calculating equilibrium properties of these systems by computer simulation. These facts are clearly viewed in molecular dynamics (MD) simulation. . There exist motions with different time scales and long relaxation times appear; therefore very long runs used to be required to get good descriptions of some properties. Such a situation can be partially improved by including some constraints in MD simulation. This procedure is done by freezing the fasterinternal degrees offreedom, 16.17 which are supposed to have little importance in the conformational properties ofthe molecules. This way it is possible to increase the time step of integration of the equations of motion, which allow us to increase the total time of integration and therefore the efficiency of the MD calculations. Monte Carlo (MC) methods do not, in principle, suffer that kind of physical limitation as far as there is not a real time involved in the sequence of configurations generated in the simulation. This fact of course leads to the loss of the dynamical information of the system. However, it is sometimes possible to design special algorithms adapted to specific problems. IB Such a possibility let us study systems in which MD is of little use to get accurate values of some equilibrium properties. Reptation techniques 1