Aurélien Perera | Sorbonne University (original) (raw)

Papers by Aurélien Perera

Physical Chemistry Chemical Physics, 2021

The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and co... more The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and constrained by steric hindrance is highly relevant in chemistry physics, biology and for many aspects of daily life....

The Journal of Physical Chemistry B, 2020

The X-ray scattering intensities I(k) of linear alkanols OH(CH2)n−1CH3, obtained from experiments... more The X-ray scattering intensities I(k) of linear alkanols OH(CH2)n−1CH3, obtained from experiments (methanol to 1-undecanol) and computer simulations (methanol to 1-nonanol) of different force field models, are comparatively studied, particularly in order to explain the origin and the properties of the scattering pre-peak in the k-vector range 0.3Å −1 −1Å −1. The experimental I(k) show two apparent features: the pre-peak position kP decreases with increasing n, and more intriguingly, the amplitude AP goes through a maximum at 1-butanol (n = 4). The first feature is well reproduced by all force field models, while the second shows a strong model dependence. The simulations reveal various shapes of clusters of the hydroxyl head-group, from n > 2. kP is directly related to the size of the meta-objects corresponding to such clusters surrounded by their alkyl tails. The explanation of the Ap turnover at n = 4 is more involved. The analysis of the atom-atom structure factors indicates that the pre-peaks arise from an incomplete cancellation between two types of contributions from the various atom-atom structure factors: positive contributions from atoms part of the head group (essentially hydroxyl group), and a mostly

The Journal of Chemical Physics, 2019

Large-scale molecular dynamics (MD) simulations are reported for aqueous t-butanol (TBA) solution... more Large-scale molecular dynamics (MD) simulations are reported for aqueous t-butanol (TBA) solutions. The CHARMM generalized force field (CGenFF) for TBA is combined with the TIP4P/2005 model for water. Unlike many other common TBA models, the CGenFF model is miscible with water in all proportions at 300 K. The main purpose of this work is to investigate the existence and nature of microheterogeneous structure in aqueous TBA solutions. Our simulations of large systems (128000 and 256000 particles) at TBA mole fractions of 0.06 and 0.1 clearly reveal the existence of long-range correlations (> 10 nm) that show significant variations on long time scales (∼ 50 ns). We associate these long-range, slowly varying correlations with the existence of supramolecular, domain-like structures that consist of TBA-rich and water-rich regions. This structure is always present but continually changing in time, giving rise to long-range, slowly varying pair correlation functions. We find that this behavior appears to have little influence on the single particle dynamics; the diffusion coefficients of both TBA and water molecules lie in the usual liquid state regime, and mean square displacements provide no indication of anomalous diffusion. Using our large system simulations, we are able to reliably calculate small angle x-ray scattering (SAXS) and small angle neutron scattering (SANS) spectra, except at very low wave vector, and the results agree well with recent experiments. However, the present paper shows that simulation of the relatively simple TBA/water system remains challenging. This is particularly true if one wishes to obtain properties such as Kirkwood-Buff factors, or scattering functions at low wave vector, which strongly depend on the long-range behavior of the pair correlations.

The Journal of Chemical Physics, 2019

A two-component interaction model is introduced herein, which allows to describe macroscopic misc... more A two-component interaction model is introduced herein, which allows to describe macroscopic miscibility with various modes of tunable micro-segregation, ranging from phase separation to micro-segregation, and in excellent agreement for structural quantities obtained from simulations and the liquid state hypernetted-chain like integral equation theory. The model is based on the conjecture that the many-body correlation bridge function term in the closure relation can be divided into one part representing the segregation effects, which are modeled herein, and the usual part representing random many body fluctuations. Furthermore, the model allows to fully neglect these second contributions, thus increasing the agreement between the simulations and the theory. The analysis of the retained part of the many body correlations gives important clues about how to model the many body bridge functions for more realistic systems exhibiting micro-segregation, such as aqueous mixtures.

The Journal of Physical Chemistry, 1985

Physical chemistry chemical physics : PCCP, Jan 4, 2017

The structural properties of ionic liquids and alcohols are viewed under the charge ordering proc... more The structural properties of ionic liquids and alcohols are viewed under the charge ordering process as a common basis to explain the peculiarity of their radiation scattering properties, namely the presence, or absence, of a scattering pre-peak. Through the analysis of models, it is shown that the presence, or absence, of a radiation scattering pre-peak is principally related to the symmetry breaking, or not, of the global charge order, induced by the peculiarities of the molecular shapes. This symmetry breaking is achieved, in practice, by the emergence of specific types of clusters, which manifests how the global charge order has changed into a local form. Various atom-atom correlations witness the symmetry breaking induced by this re organization, and this is manifested into a pre-peak in the structure factor. This approach explains why associated liquids such as water do not show a scattering pre-peak. It also explains under which conditions core-soft models can mimic associati...

The Journal of Chemical Physics, 2016

Methanol-ethanol mixtures under ambient conditions of temperature and pressure are studied by com... more Methanol-ethanol mixtures under ambient conditions of temperature and pressure are studied by computer simulations, with the aim to sort out how the ideality of this type of mixtures differs from that of a textbook example of an ideal mixture. This study reveals two types of ideality, one which is related to simple disorder, such as in benzene-cyclohexane mixtures, and another found in complex disorder mixtures of associated liquids. It underlines the importance of distinguishing between concentration fluctuations, which are shared by both types of systems, and the structural heterogeneity, which characterises the second class of disorder. Methanol-1propanol mixtures are equally studied and show a quasi-ideality with many respect comparable to that of the methanolethanol mixtures, hinting at the existence of a super-ideality in neat mono-ol binary mixtures, driven essentially by the strong hydrogen bonding and underlying hydroxyl group clustering.

The Journal of Chemical Physics, 2016

The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature ... more The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature range 300 K-120 K, is studied with computer simulations, from the static structural point of view. The structural heterogeneity of water is reinforced at lower temperatures, as witnessed by a pre-peak in the oxygen-oxygen structure factor. Water tends to form predominantly chain-like clusters at lower temperatures and smaller concentrations. Methanol domains have essentially the same chain-like cluster structure as the pure liquid at high concentrations and becomes monomeric at smaller ones. Concentration fluctuations decrease with temperature, leading to quasi-ideal Kirkwood-Buff integrals, despite the enhanced molecular interactions, which we interpret as the signature of non-interacting segregated water and methanol clusters. This study throws a new light on the nature of the micro-heterogeneous structure of this mixture: the domain segregation is essentially based on the appearance of linear water clusters, unlike other alcohol aqueous mixtures, such as with propanol or butanol, where the water domains are more bulky.

Journal de Physique Lettres, 1983

2014 L'influence de l'échange monomères-micelles sur les propriétés de transport des systèmes mic... more 2014 L'influence de l'échange monomères-micelles sur les propriétés de transport des systèmes micellaires à forte concentration micellaire critique est mise en évidence. La diffusion de la lumière de l'octanoate de sodium et de l'hexylsulfate de sodium est analysée à partir d'un nouveau modèle cinétique en tenant compte des interactions micelles-micelles. Abstract. 2014 For micellar systems having a high critical micellar concentration, it is shown that the monomer-micelle exchange makes a significant contribution to the diffusion processes. Practical examples are micelles of sodium octanoate and sodium hexyl sulphate. Their diffusion coefficients are analysed in the framework of a kinetic model which includes the effect of intermicellar interactions.

Molecular Dynamics - Studies of Synthetic and Biological Macromolecules, 2012

Physical Review E, 2001

The stability of binary fluid mixtures, with respect to a demixing transition, is examined within... more The stability of binary fluid mixtures, with respect to a demixing transition, is examined within the framework of the geometrical approximation of the direct correlation for hard nonspherical particles. In this theory, the direct correlation function is essentially written in terms of the geometrical properties of the individual molecules, and those of the overlap region between two different molecules, taken at fixed separation and orientations. Within the present theory, the demixing spinodal line in the (rho(1),rho(2)) concentration plane is obtained analytically, and shown to be a quadratic function of the total packing fraction and the compositions. The theory is applied herein to binary mixtures of hard spherocylinders in the isotropic phase. Isotropic fluid-fluid demixing can be predicted for a large variety of sizes and aspect ratios, and the necessary condition for entropic demixing is a sufficiently large thickness difference between the two particles that belong to each of the fluids in the mixture. As the theory reduces exactly to the Percus-Yevick approximation for a hard sphere mixture, accordingly it will not predict fluid-fluid demixing for this particular case. Demixing is also forbidden in two other cases; for a mixture of spherocylinders and small spheres, and for mixtures of equally thin spherocylinders. The influence and competition of an ordering instability on the demixing is also examined. The ordering of a fluid will always be displaced toward higher packing fractions by the addition of a nonordering fluid, and in some cases the entropic demixing can dominate the entire fluid range. Although the present theory merges exactly with the correct Onsager limit, it is shown that, for intermediate cases, the results can be significantly different from predictions of Onsager type approaches. These discrepancies are analyzed in particular for the needle plus spherocylinder mixture. Finally, in view of the nature of the theory, it is conjectured that the predicted demixing densities values are rather upper bounds to what should be expected.

Vibrational Spectroscopy, 2012

ABSTRACT Mixing of two hydrogen-bonded liquids may lead to significant composition dependent chan... more ABSTRACT Mixing of two hydrogen-bonded liquids may lead to significant composition dependent changes of liquid microscopic structure, which in turn will be reflected by changes of the corresponding thermodynamic, thermophysical and spectroscopic properties. For the liquid system {xEtOHC2H5OH+(1−xEtOH)H2O} at ambient temperatures and pressures, we show that major structural rearrangements occur in the composition range of 0.15

Molecular Physics, 2009

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Molecular Physics, 1998

... 93, NO. 4, 649ą661 On the linear hard sphere chain Ŋ uids By ANTOINE CHAMOUX and AURE LIEN P... more ... 93, NO. 4, 649ą661 On the linear hard sphere chain Ŋ uids By ANTOINE CHAMOUX and AURE LIEN PERERA Laboratoire de Physique The orique des Liquidesē , Universite Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05, France ...

The Journal of Chemical Physics, 1989

ABSTRACT The hypernetted‐chain (HNC) approximation is solved for fluids of dipolar hard ellipsoid... more ABSTRACT The hypernetted‐chain (HNC) approximation is solved for fluids of dipolar hard ellipsoids and the structural, thermodynamic, and dielectric properties of the isotropic phase are discussed in some detail. Both prolate and oblate particles are considered and the isotropic–nematic transition is investigated using density functional theory (DFT). For fluids of prolate particles dipolar forces are found to have a significant effect upon the isotropic–nematic transition which occurs at lower densities as the dipole moment is increased. For the oblate case the dipolar interactions have only a very small, if any, influence upon the isotropic–nematic transition density. For both prolate and oblate particles the present HNC/DFT calculations do not predict ferroelectric nematic phases.

The Journal of Chemical Physics, 1987

ABSTRACT In this paper we describe a general approach which allows the hypernetted chain (HNC) an... more ABSTRACT In this paper we describe a general approach which allows the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories to be solved numerically for fluids of hard nonspherical particles. Explicit results are given for fluids of hard ellipsoids of revolution and comparisons are made with recent Monte Carlo calculations. It is found that for dense systems of highly anisotropic ellipsoids the HNC and PY closures give significantly different results. The HNC theory is superior predicting the existance of a nematic phase in qualitative agreement with computer simulations. The PY approximation strongly and erroneously suggests that the isotropic phase is stable throughout the liquid regime.

The Journal of Chemical Physics, 1991

ABSTRACT We investigate the structural and thermodynamic properties of the isotropic phase of the... more ABSTRACT We investigate the structural and thermodynamic properties of the isotropic phase of the hard ellipse liquid for several length‐to‐breadth ratios (2,4,6), using the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories. A comparison with the recent simulations of Cuesta and Frenkel [Phys. Rev. A 42, 2126 (1990)] is made. Satisfactory agreement is found with PY theory for small aspect ratios, while for larger ones, HNC results become superior. In addition, HNC (but not PY) predicts the orientational instability of the isotropic phase at a finite density for systems of aspect ratios 4 and 6, in good agreement with computer simulation results. In order to investigate the order of the orientational phase transition, density functional theories (DFT) calculations are carried out using as input the direct correlation functions of the isotropic liquid obtained in this work. No first‐order transition is found within the version of DFT used herein.

The Journal of Chemical Physics, 1997

In order to understand the translational and rotational motion in dense molecular liquids, detail... more In order to understand the translational and rotational motion in dense molecular liquids, detailed molecular dynamics simulations of Lennard–Jones ellipsoids have been carried out for three different values of the aspect ratio κ. For ellipsoids with an aspect ratio equal to 2, the ...

The Journal of Chemical Physics, 1998

Detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out to inve... more Detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out to investigate the emergence of criticality in the single-particle orientational relaxation near the isotropic–nematic (IN) phase transition. The simulations show a sudden appearance of a ...

Physical Chemistry Chemical Physics, 2021

The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and co... more The understanding of the microstructure of associated liquids promoted by hydrogen-bonding and constrained by steric hindrance is highly relevant in chemistry physics, biology and for many aspects of daily life....

The Journal of Physical Chemistry B, 2020

The X-ray scattering intensities I(k) of linear alkanols OH(CH2)n−1CH3, obtained from experiments... more The X-ray scattering intensities I(k) of linear alkanols OH(CH2)n−1CH3, obtained from experiments (methanol to 1-undecanol) and computer simulations (methanol to 1-nonanol) of different force field models, are comparatively studied, particularly in order to explain the origin and the properties of the scattering pre-peak in the k-vector range 0.3Å −1 −1Å −1. The experimental I(k) show two apparent features: the pre-peak position kP decreases with increasing n, and more intriguingly, the amplitude AP goes through a maximum at 1-butanol (n = 4). The first feature is well reproduced by all force field models, while the second shows a strong model dependence. The simulations reveal various shapes of clusters of the hydroxyl head-group, from n > 2. kP is directly related to the size of the meta-objects corresponding to such clusters surrounded by their alkyl tails. The explanation of the Ap turnover at n = 4 is more involved. The analysis of the atom-atom structure factors indicates that the pre-peaks arise from an incomplete cancellation between two types of contributions from the various atom-atom structure factors: positive contributions from atoms part of the head group (essentially hydroxyl group), and a mostly

The Journal of Chemical Physics, 2019

Large-scale molecular dynamics (MD) simulations are reported for aqueous t-butanol (TBA) solution... more Large-scale molecular dynamics (MD) simulations are reported for aqueous t-butanol (TBA) solutions. The CHARMM generalized force field (CGenFF) for TBA is combined with the TIP4P/2005 model for water. Unlike many other common TBA models, the CGenFF model is miscible with water in all proportions at 300 K. The main purpose of this work is to investigate the existence and nature of microheterogeneous structure in aqueous TBA solutions. Our simulations of large systems (128000 and 256000 particles) at TBA mole fractions of 0.06 and 0.1 clearly reveal the existence of long-range correlations (> 10 nm) that show significant variations on long time scales (∼ 50 ns). We associate these long-range, slowly varying correlations with the existence of supramolecular, domain-like structures that consist of TBA-rich and water-rich regions. This structure is always present but continually changing in time, giving rise to long-range, slowly varying pair correlation functions. We find that this behavior appears to have little influence on the single particle dynamics; the diffusion coefficients of both TBA and water molecules lie in the usual liquid state regime, and mean square displacements provide no indication of anomalous diffusion. Using our large system simulations, we are able to reliably calculate small angle x-ray scattering (SAXS) and small angle neutron scattering (SANS) spectra, except at very low wave vector, and the results agree well with recent experiments. However, the present paper shows that simulation of the relatively simple TBA/water system remains challenging. This is particularly true if one wishes to obtain properties such as Kirkwood-Buff factors, or scattering functions at low wave vector, which strongly depend on the long-range behavior of the pair correlations.

The Journal of Chemical Physics, 2019

A two-component interaction model is introduced herein, which allows to describe macroscopic misc... more A two-component interaction model is introduced herein, which allows to describe macroscopic miscibility with various modes of tunable micro-segregation, ranging from phase separation to micro-segregation, and in excellent agreement for structural quantities obtained from simulations and the liquid state hypernetted-chain like integral equation theory. The model is based on the conjecture that the many-body correlation bridge function term in the closure relation can be divided into one part representing the segregation effects, which are modeled herein, and the usual part representing random many body fluctuations. Furthermore, the model allows to fully neglect these second contributions, thus increasing the agreement between the simulations and the theory. The analysis of the retained part of the many body correlations gives important clues about how to model the many body bridge functions for more realistic systems exhibiting micro-segregation, such as aqueous mixtures.

The Journal of Physical Chemistry, 1985

Physical chemistry chemical physics : PCCP, Jan 4, 2017

The structural properties of ionic liquids and alcohols are viewed under the charge ordering proc... more The structural properties of ionic liquids and alcohols are viewed under the charge ordering process as a common basis to explain the peculiarity of their radiation scattering properties, namely the presence, or absence, of a scattering pre-peak. Through the analysis of models, it is shown that the presence, or absence, of a radiation scattering pre-peak is principally related to the symmetry breaking, or not, of the global charge order, induced by the peculiarities of the molecular shapes. This symmetry breaking is achieved, in practice, by the emergence of specific types of clusters, which manifests how the global charge order has changed into a local form. Various atom-atom correlations witness the symmetry breaking induced by this re organization, and this is manifested into a pre-peak in the structure factor. This approach explains why associated liquids such as water do not show a scattering pre-peak. It also explains under which conditions core-soft models can mimic associati...

The Journal of Chemical Physics, 2016

Methanol-ethanol mixtures under ambient conditions of temperature and pressure are studied by com... more Methanol-ethanol mixtures under ambient conditions of temperature and pressure are studied by computer simulations, with the aim to sort out how the ideality of this type of mixtures differs from that of a textbook example of an ideal mixture. This study reveals two types of ideality, one which is related to simple disorder, such as in benzene-cyclohexane mixtures, and another found in complex disorder mixtures of associated liquids. It underlines the importance of distinguishing between concentration fluctuations, which are shared by both types of systems, and the structural heterogeneity, which characterises the second class of disorder. Methanol-1propanol mixtures are equally studied and show a quasi-ideality with many respect comparable to that of the methanolethanol mixtures, hinting at the existence of a super-ideality in neat mono-ol binary mixtures, driven essentially by the strong hydrogen bonding and underlying hydroxyl group clustering.

The Journal of Chemical Physics, 2016

The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature ... more The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature range 300 K-120 K, is studied with computer simulations, from the static structural point of view. The structural heterogeneity of water is reinforced at lower temperatures, as witnessed by a pre-peak in the oxygen-oxygen structure factor. Water tends to form predominantly chain-like clusters at lower temperatures and smaller concentrations. Methanol domains have essentially the same chain-like cluster structure as the pure liquid at high concentrations and becomes monomeric at smaller ones. Concentration fluctuations decrease with temperature, leading to quasi-ideal Kirkwood-Buff integrals, despite the enhanced molecular interactions, which we interpret as the signature of non-interacting segregated water and methanol clusters. This study throws a new light on the nature of the micro-heterogeneous structure of this mixture: the domain segregation is essentially based on the appearance of linear water clusters, unlike other alcohol aqueous mixtures, such as with propanol or butanol, where the water domains are more bulky.

Journal de Physique Lettres, 1983

2014 L'influence de l'échange monomères-micelles sur les propriétés de transport des systèmes mic... more 2014 L'influence de l'échange monomères-micelles sur les propriétés de transport des systèmes micellaires à forte concentration micellaire critique est mise en évidence. La diffusion de la lumière de l'octanoate de sodium et de l'hexylsulfate de sodium est analysée à partir d'un nouveau modèle cinétique en tenant compte des interactions micelles-micelles. Abstract. 2014 For micellar systems having a high critical micellar concentration, it is shown that the monomer-micelle exchange makes a significant contribution to the diffusion processes. Practical examples are micelles of sodium octanoate and sodium hexyl sulphate. Their diffusion coefficients are analysed in the framework of a kinetic model which includes the effect of intermicellar interactions.

Molecular Dynamics - Studies of Synthetic and Biological Macromolecules, 2012

Physical Review E, 2001

The stability of binary fluid mixtures, with respect to a demixing transition, is examined within... more The stability of binary fluid mixtures, with respect to a demixing transition, is examined within the framework of the geometrical approximation of the direct correlation for hard nonspherical particles. In this theory, the direct correlation function is essentially written in terms of the geometrical properties of the individual molecules, and those of the overlap region between two different molecules, taken at fixed separation and orientations. Within the present theory, the demixing spinodal line in the (rho(1),rho(2)) concentration plane is obtained analytically, and shown to be a quadratic function of the total packing fraction and the compositions. The theory is applied herein to binary mixtures of hard spherocylinders in the isotropic phase. Isotropic fluid-fluid demixing can be predicted for a large variety of sizes and aspect ratios, and the necessary condition for entropic demixing is a sufficiently large thickness difference between the two particles that belong to each of the fluids in the mixture. As the theory reduces exactly to the Percus-Yevick approximation for a hard sphere mixture, accordingly it will not predict fluid-fluid demixing for this particular case. Demixing is also forbidden in two other cases; for a mixture of spherocylinders and small spheres, and for mixtures of equally thin spherocylinders. The influence and competition of an ordering instability on the demixing is also examined. The ordering of a fluid will always be displaced toward higher packing fractions by the addition of a nonordering fluid, and in some cases the entropic demixing can dominate the entire fluid range. Although the present theory merges exactly with the correct Onsager limit, it is shown that, for intermediate cases, the results can be significantly different from predictions of Onsager type approaches. These discrepancies are analyzed in particular for the needle plus spherocylinder mixture. Finally, in view of the nature of the theory, it is conjectured that the predicted demixing densities values are rather upper bounds to what should be expected.

Vibrational Spectroscopy, 2012

ABSTRACT Mixing of two hydrogen-bonded liquids may lead to significant composition dependent chan... more ABSTRACT Mixing of two hydrogen-bonded liquids may lead to significant composition dependent changes of liquid microscopic structure, which in turn will be reflected by changes of the corresponding thermodynamic, thermophysical and spectroscopic properties. For the liquid system {xEtOHC2H5OH+(1−xEtOH)H2O} at ambient temperatures and pressures, we show that major structural rearrangements occur in the composition range of 0.15

Molecular Physics, 2009

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Molecular Physics, 1998

... 93, NO. 4, 649ą661 On the linear hard sphere chain Ŋ uids By ANTOINE CHAMOUX and AURE LIEN P... more ... 93, NO. 4, 649ą661 On the linear hard sphere chain Ŋ uids By ANTOINE CHAMOUX and AURE LIEN PERERA Laboratoire de Physique The orique des Liquidesē , Universite Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Cedex 05, France ...

The Journal of Chemical Physics, 1989

ABSTRACT The hypernetted‐chain (HNC) approximation is solved for fluids of dipolar hard ellipsoid... more ABSTRACT The hypernetted‐chain (HNC) approximation is solved for fluids of dipolar hard ellipsoids and the structural, thermodynamic, and dielectric properties of the isotropic phase are discussed in some detail. Both prolate and oblate particles are considered and the isotropic–nematic transition is investigated using density functional theory (DFT). For fluids of prolate particles dipolar forces are found to have a significant effect upon the isotropic–nematic transition which occurs at lower densities as the dipole moment is increased. For the oblate case the dipolar interactions have only a very small, if any, influence upon the isotropic–nematic transition density. For both prolate and oblate particles the present HNC/DFT calculations do not predict ferroelectric nematic phases.

The Journal of Chemical Physics, 1987

ABSTRACT In this paper we describe a general approach which allows the hypernetted chain (HNC) an... more ABSTRACT In this paper we describe a general approach which allows the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories to be solved numerically for fluids of hard nonspherical particles. Explicit results are given for fluids of hard ellipsoids of revolution and comparisons are made with recent Monte Carlo calculations. It is found that for dense systems of highly anisotropic ellipsoids the HNC and PY closures give significantly different results. The HNC theory is superior predicting the existance of a nematic phase in qualitative agreement with computer simulations. The PY approximation strongly and erroneously suggests that the isotropic phase is stable throughout the liquid regime.

The Journal of Chemical Physics, 1991

ABSTRACT We investigate the structural and thermodynamic properties of the isotropic phase of the... more ABSTRACT We investigate the structural and thermodynamic properties of the isotropic phase of the hard ellipse liquid for several length‐to‐breadth ratios (2,4,6), using the hypernetted chain (HNC) and Percus–Yevick (PY) integral equation theories. A comparison with the recent simulations of Cuesta and Frenkel [Phys. Rev. A 42, 2126 (1990)] is made. Satisfactory agreement is found with PY theory for small aspect ratios, while for larger ones, HNC results become superior. In addition, HNC (but not PY) predicts the orientational instability of the isotropic phase at a finite density for systems of aspect ratios 4 and 6, in good agreement with computer simulation results. In order to investigate the order of the orientational phase transition, density functional theories (DFT) calculations are carried out using as input the direct correlation functions of the isotropic liquid obtained in this work. No first‐order transition is found within the version of DFT used herein.

The Journal of Chemical Physics, 1997

In order to understand the translational and rotational motion in dense molecular liquids, detail... more In order to understand the translational and rotational motion in dense molecular liquids, detailed molecular dynamics simulations of Lennard–Jones ellipsoids have been carried out for three different values of the aspect ratio κ. For ellipsoids with an aspect ratio equal to 2, the ...

The Journal of Chemical Physics, 1998

Detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out to inve... more Detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out to investigate the emergence of criticality in the single-particle orientational relaxation near the isotropic–nematic (IN) phase transition. The simulations show a sudden appearance of a ...