The phase diagram of the two center Lennard-Jones model as obtained from computer simulation and Wertheim’s thermodynamic perturbation theory

Vega, Carlos; McBride, Carl; Miguel, Enrique de; Blas, Felipe J.; Galindo, Amparo

doi:10.1063/1.1572811

Cited by 34 publications

(36 citation statements)

References 64 publications

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“…Closely related apolar dumbbell systems show formation of an amorphous solid phase at similar temperatures [43]. We also observe solidification in our systems at low temperature and this is a likely explanation for these peaks.…”

Section: Resultssupporting

confidence: 77%

Thermo-molecular orientation effects in fluids of dipolar dumbbells

Daub

Åstrand

Bresme

2014

Phys. Chem. Chem. Phys.

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We use molecular dynamics simulations in applied thermal gradients to study thermomolecular orientation (TMO) of size-asymmetric dipolar dumbbells with different molecular dipole moments.We find that the direction of the TMO is the same as in apolar dumbbells of the same size, i.e. the smaller atom in the dumbbell tends to orient towards the colder temperature. The ratio of the electrical polarization to the magnitude of the thermal gradient does not vary much with the magnitude of the molecular dipole moment. We also investigate a novel second order TMO that persists even in size-symmetric dipolar dumbbells where molecules have a slight tendency to orient perpendicular to the gradient except very close to the hot region, where (anti-)parallel orientations are preferred. Finally, we investigate rotational correlation functions and characteristic rotational times in these systems in an attempt to model possible spectroscopic signatures of TMO in experiments. Although we cannot detect any difference in integrated rotational times between equilibrium simulations and simulations in a thermal gradient, more careful modelling of the anisotropic rotational dynamics in the thermal gradient may be more successful.

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Section: Resultssupporting

confidence: 77%

Thermo-molecular orientation effects in fluids of dipolar dumbbells

Daub

Åstrand

Bresme

2014

Phys. Chem. Chem. Phys.

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“…equation (65) is useful not only for ice but for other disordered solids as well. In fact it can be applied successfully [158,159,32,160,38] to tangent dimers, formed by two tangent spheres, where Nagle [161] has estimated Ω, and for fully flexible hard sphere chains [42](where Flory and Huggins [162,163] have estimated Ω).…”

Section: Einstein Crystal Calculations For Disordered Systemsmentioning

confidence: 99%

“…Of course for a simple fluid (HS, LJ) there are no orientational degrees of freedom so that in the Einstein molecule approach, atom 1 is fixed. Fixing the position of one molecule avoids the quasi-divergence of the integrand of equation (38) when the coupling parameter λ tends to zero. The computational implementation of the method as well as the derivation of the main equations is rather simple.…”

Section: The Einstein Molecule Approachmentioning

confidence: 99%

“…Repeating the calculation at different thermodynamic conditions then it is possible to determine the phase diagram for a certain potential model. This route has often been used in the past for a number of simple models including hard ellipsoids [28], the Gay Berne model [29], the hard Gaussian [30], hard dumbbells [31,32,33,34], hard spherocylinders [35,36,37], diatomic LJ models [38,39,40], quadrupolar hard dumbells [41], hard flexible chains [42,43], linear rigid chains [44,45], chiral systems [46], quantum hard spheres [47], primitive models of water [48], electrolytes [49,50], benzene [51,52], propane [53] and idealised models of colloidal particles [54,55,56,50,57,58]. Some of the main findings of this research (up to 2000) have been reviewed by Monson and Kofke [5].…”

Section: Introductionmentioning

confidence: 99%

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Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Vega¹,

Sanz

Abascal

et al. 2008

J. Phys.: Condens. Matter

274

452

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Abstract. In this review we focus on the determination of phase diagrams by computer simulation with particular attention to the fluid-solid and solid-solid equilibria. The methodology to compute the free energy of solid phases will be discussed. In particular, the Einstein crystal and Einstein molecule methodologies are described in a comprehensive way. It is shown that both methodologies yield the same free energies and that free energies of solid phases present noticeable finite size effects. In fact this is the case for hard spheres in the solid phase. Finite size corrections can be introduced, although in an approximate way, to correct for the dependence of the free energy on the size of the system. The computation of free energies of solid phases can be extended to molecular fluids. The procedure to compute free energies of solid phases of water (ices) will be described in detail. The free energies of ices Ih, II, III, IV, V, VI, VII, VIII, IX, XI and XII will be presented for the SPC/E and TIP4P models of water. Initial coexistence points leading to the determination of the phase diagram of water for these two models will be provided. Other methods to estimate the melting point of a solid, as the direct fluid-solid coexistence or simulations of the free surface of the solid will be discussed. It will be shown that the melting points of ice Ih for several water models, obtained from free energy calculations, direct coexistence simulations and free surface simulations, agree within their statistical uncertainty. Phase diagram calculations can indeed help to improve potential models of molecular fluids. For instance, for water, the potential model TIP4P/2005 can be regarded as an improved version of TIP4P. Here we will review some recent work on the phase diagram of the simplest ionic model, the restricted primitive model. Although originally devised to describe ionic liquids, the model is becoming quite popular to describe the behaviour of charged colloids. Besides the possibility of obtaining fluid-solid equilibria for simple protein models will be discussed. In these primitive models, the protein is described by a spherical potential with certain anisotropic bonding sites (patchy sites).

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AbstractBy using canonical Monte Carlo simulation, the liquid-vapor phase diagram, surface tension, interface width, and pressure for the Mie(n,m) model fluids are calculated for six pairs of parameters m and n. It is shown that after certain re-scaling of fluid density the corresponding states rule can be applied for the calculations of the thermodynamic properties of the Mie model fluids, and for some real substances.

PACS numbers:1 Among the intermolecular effective interaction potentials, the Lennard-Jones one is by far the most widely used for approximating the physics of simple nonpolar molecules in all phases of matter [1,2,3,4,5,6,7,8,9,10,11,12]. The attractiveness of the LJ model is mainly due to its more convenient mathematical form than to its accuracy in representing the properties of real fluids.

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mentioning

confidence: 99%

Some universal trends of the Mie(n,m) fluid thermodynamics

2008

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By using canonical Monte Carlo simulation, the liquid-vapor phase diagram, surface tension, interface width, and pressure for the Mie(n,m) model fluids are calculated for six pairs of parameters m and n. It is shown that after certain re-scaling of fluid density the corresponding states rule can be applied for the calculations of the thermodynamic properties of the Mie model fluids, and for some real substances. PACS numbers:1 Among the intermolecular effective interaction potentials, the Lennard-Jones one is by far the most widely used for approximating the physics of simple nonpolar molecules in all phases of matter [1,2,3,4,5,6,7,8,9,10,11,12]. The attractiveness of the LJ model is mainly due to its more convenient mathematical form than to its accuracy in representing the properties of real fluids. Some modifications of the LJ potential, like exp-6 [11,12] or the family of Mie(n,m) potentials [13,14,15], have shown to be useful for the description of thermodynamic and dynamic properties of some real substances. The Mie(n,m) pair potential, which is just a general form of the LJ model, is defined as,where r is the interparticle distance reduced by the particle diameter, which is chosen to be the unit length, σ = 1; ǫ is the well depth. The temperature of the system is defined asRecently, both theory and molecular simulations have been used to compute the properties of the Mie(n,m) model fluids [9,10,11,12,15,16,17,18,19,20,21,22]. The Mie fluid potential is often said to be short-ranged, however, for any finite system size, the potential is not rigorously zero at a distance of the half box length where the potential is typically truncated. Some approaches were proposed for dealing with the long-range tail of the potential [3,10]. Perhaps, due to the commonly used procedure of potential cut-off during molecular It is well accepted that CS rule permits the prediction of unknown properties of many fluids from the known properties of a few [1,23,24,25,26]. Its application to the model potential fluids allows to avoid the usually timeconsuming molecular simulations, and also 2 makes possible the utilization of some important developments in statistical mechanics which would otherwise be prohibited by computational difficulties. Firstly the CS rule was derived by van der Waals based on his well-known equation of state,where the variables were reduced by their critical values, ρ R = ρ/ρ c ; (reduced number density or inverse molar volume), T R = T /T c (reduced temperature), and P R = P/P c (reduced pressure). Later, the CS principle was extended by introducing additional parameters to the study of various types of molecular fluids [1]. Thus, in general, macroscopic CS law states that all substances obey the same equation of state in terms of the reduced variables, or, in other words, the state of a system may be described by any two of the three variables:pressure, density, and temperature. In this work we study the systems with two particular cases of the potential (1). Namely, the one-parameter Mie(2m,m) ...

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The phase diagram of the two center Lennard-Jones model as obtained from computer simulation and Wertheim’s thermodynamic perturbation theory

Cited by 34 publications

References 64 publications

Thermo-molecular orientation effects in fluids of dipolar dumbbells

Thermo-molecular orientation effects in fluids of dipolar dumbbells

Determination of phase diagrams via computer simulation: methodology and applications to water, electrolytes and proteins

Some universal trends of the Mie(n,m) fluid thermodynamics

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