Jayashree Saha - Academia.edu (original) (raw)

Papers by Jayashree Saha

arXiv (Cornell University), Jan 30, 2020

To understand mechanism of cell-membrane compartmentalization, we studied coarse-grained model sy... more To understand mechanism of cell-membrane compartmentalization, we studied coarse-grained model systems consisting of lipid and cholesterol molecules. Cholesterol plays crucial role in lateral phase segregation in the bilayered lipid membrane to form cholesterol rich liquid ordered domains, termed as 'rafts'. In this NVT Molecular Dynamics simulation study, we have investigated the role of cholesterol in raft-like domain formation. The study reveals that the strength of cholesterol interaction is an important factor behind the phase segregation to form cholesterol rich domains, whereas, the relative dipolar strength of lipid and cholesterol molecules controls the formation of multi-bilayered stack.

arXiv (Cornell University), Dec 3, 2019

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral... more We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

The Journal of Physical Chemistry B

A simple, dual-site model of bolaamphiphiles (bolaforms or bipolar amphiphiles) is developed base... more A simple, dual-site model of bolaamphiphiles (bolaforms or bipolar amphiphiles) is developed based on an earlier single-site model of (monopolar) amphiphiles [S. Dey, J. Saha, Phys. Rev. E 95, 023315 (2017)]. The model incorporates aqueous environment (both hydrophobic effect and hydration force) in its anisotropic site-site interactions, thus obviating the need to simulate solvent particles explicitly. This economy of sites and the absence of explicit solvent particles enable molecular dynamics simulations of bolaamphiphiles to achieve mesoscopic length and timescales unattainable by any bead-spring model or explicit solvent computations. The model applies to generic bolas only, since the gain in scale can only be obtained by sacrificing the resolution of detailed molecular structure. Thanks to dual-sites, however, (as opposed to a singlesite model) our model can incorporate the essential flexibility of bolas that leads to their U-conformers. The model bolas show successful selfassembly into experimentally observed nano-structures like micelles, rods, lamellae etc. and retain fluidity in very stable monolayers. Presence of membrane-spanning model bolas in bilayers of model monopolar amphiphiles increases the stability and impermeability of the lamellar phase. Model bolas are also seen to be less diffusive and to produce thicker layers compared to their monopolar counterparts. Rigid model bolas, though achiral themselves, show self-assembly into helical rods. As all these observations agree with the well-known key characteristics of archaeal lipids and synthetic bolaamphiphiles, our model promises to be effective for studies of bolas in context of biomimetics, drug-delivery and low molecular weight hydrogelators. To the best of our knowledge, no other single or dual-site, solvent-free model for bolas has been reported thus far.

Computationally, low-resolution coarse-grained models provide the most viable means for simulatin... more Computationally, low-resolution coarse-grained models provide the most viable means for simulating the large length and time scales associated with mesoscopic phenomena. Moreover, since lyotropic phases in solution may contain high solvent to amphiphile ratio, implicit solvent models are appropriate for many purposes. By modifying the well-known Gay-Berne potential with an imposed uni-directionality and a longer range, we have come to a simple single-site model amphiphile that can rapidly self-assemble to give diverse lyotropic phases without the explicit incorporation of solvent particles. The model represents a tuneable packing parameter that manifests in the spontaneous curvature of amphiphile aggregates. Apart from large scale simulations (e.g. the study of self-assembly, amphiphile mixing, domain formation etc.) this novel, non-specific model may be useful for suggestive pilot projects with modest computational resources. No such self-assembling, single-site amphiphile model ha...

JCIS Open, 2021

Implicit solvent, coarse-grained models with pairwise interactions can access the largest length ... more Implicit solvent, coarse-grained models with pairwise interactions can access the largest length and time scales in molecular dynamics simulations, owing to the absence of computationally expensive interactions with a huge number of solvent particles, the smaller number of interaction sites in the model molecules, and the lack of fast sub-molecular degrees of freedom. Without an explicit solvent, the solvent mediated effects, e.g. the hydrophobic effect and the hydration force, are mimicked entirely through the interactions between the model molecules. In this paper, we describe a maximally coarse-grained model for lipids in implicit water. The model is called SiMPLISTIC, which is an acronym for 'Single-site Model with Pairwise interaction for Lipids in Implicit Solvent with Tuneable Intrinsic Curvature'. SiMPLISTIC lipids rapidly self-assemble into realistic nonlamellar and lamellar phases such as inverted micelles and bilayers, the spontaneous curvature of the phase being determined by a single free parameter of the model. Model membrane simulations with lamellar SiMPLISTIC lipids show satisfactory fluid and gel phases with no interdigitation or tilt. Despite being rigid molecules, SiMPLISTIC lipids can generate experimentally relevant values for the bending stiffness of model membrane bilayers with no significant interleaflet coupling. SiMPLISTIC can also simulate mixtures of lipids that differ in their packing parameter or length, the latter leading to the phenomenon of hydrophobic mismatch driven phase separation or domain formation. The model has a large scope due to its speed, conceptual and computational simplicity, and versatility. Applications may range from academic and industrial research in various lipid-based systems, such as lyotropic liquid crystals, biological and biomimetic membranes, vectors for drug and gene delivery, emulsions for cosmetic products, to education, such as teaching/learning concepts like self-assembly, polymorphism, biomembrane organization etc. through interactive molecular dynamics simulations.

Fluid Phase Equilibria, 2021

Scientific Reports, 2020

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral... more We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

DAE SOLID STATE PHYSICS SYMPOSIUM 2019, 2020

Physical Review Research, 2019

We report a computer simulation study of the phase transitional behavior of a system of chiral Ga... more We report a computer simulation study of the phase transitional behavior of a system of chiral Gay-Berne molecules embedded with a terminal dipole. In this Rapid Communication, coarse-grained modeling is done to study the influence of coupled chiral and dipolar interactions on the macroscopic liquid crystalline phase behavior. This NV T molecular dynamics simulation study presents the formation of the smectic blue phase (BP Sm), which is a comparatively recent experimentally discovered chiral phase. Our study reveals that a gradual increment of the strength of the chiral interaction brings conventional cholesteric and blue phases, whereas the addition of a dipolar interaction can induce the smectic blue phase. Moreover, we demonstrate that a further increase of dipolar strength makes novel chiral bilayer phases feasible, yet to be realized experimentally.

International Journal of Modern Physics B, 1997

The mean field model for rectangular lattice having herring-bone packing of tilted molecules has ... more The mean field model for rectangular lattice having herring-bone packing of tilted molecules has been extended to reproduce even–odd alternation in the transition temperatures in a discotic system by taking into account the specific change in layering interaction and molecular biaxiality for each member of a homologous series.

Physical Review E, 2017

We report the effect of lipid head-group dipole orientation on phase behaviour of phospholipid as... more We report the effect of lipid head-group dipole orientation on phase behaviour of phospholipid assembly. The work explains molecular-scale mechanism of ion-lipid, anesthetic-lipid interactions where reorientation of dipoles play important role in membrane potential modification. Molecular Dynamics simulations are performed to analyse structure-property relationship and dynamical behaviour of lipid biomembranes considering coarse-grained model interactions.

Physical Review B, 1994

The low value of {T,-T*)/T, =0.1%, where T, is the nematic-isotropic phase-transition temperature... more The low value of {T,-T*)/T, =0.1%, where T, is the nematic-isotropic phase-transition temperature and T is the temperature at which the light-scattering intensity diverges in the supercooled isotropic phase for the nematic-isotropic transition is a long-standing puzzle. We show in this paper that by extending the renormalization-group calculation to second order of c and, alternatively, by considering that the nematic-isotropic transition is close to the tricritical point, considerable improvement over previous results is possible.

Molecular Simulation, 2016

ABSTRACT A soft ellipsoid contact potential model for a pair of biaxial ellipsoidal molecules is ... more ABSTRACT A soft ellipsoid contact potential model for a pair of biaxial ellipsoidal molecules is proposed which considers the configuration dependent energy anisotropy explicitly along with their geometrical aspects. We performed Molecular Dynamics simulation study to generate both biaxial smectic and nematic phases using this new potential.

Physics Letters A, 1992

ABSTRACT A smectic-nematic-isotropic phase transition sequence is reproduced in a 10×10×10 system... more ABSTRACT A smectic-nematic-isotropic phase transition sequence is reproduced in a 10×10×10 system. The pair interaction assumed is purely anisotropic and attractive. Temperature variations of order parameters show qualitatively the same features as those in the McMillan model.

Physical Review E, 2014

The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absenc... more The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.

Physics Letters A, 1997

A site-site potential with a hexagonal distribution of sites with one additional site at the cent... more A site-site potential with a hexagonal distribution of sites with one additional site at the centre, which can simulate disc-like molecules, is presented. To mimic this site-site potential a single-site potential has also been developed for aspherical molecules whose symmetry axis is perpendicular to the molecular plane. This potential can be used to study phases and phase transitions of disc-like liquid crystal molecules in a computationally efficient way.

Physics Letters A, 2005

We perform molecular dynamics simulation for a system of Gay–Berne molecules having two terminal ... more We perform molecular dynamics simulation for a system of Gay–Berne molecules having two terminal dipole moments to generate tilted smectic-C liquid crystal phase. We investigate the effect of dipolar orientation with respect to the long molecular axis on phase behaviour. The study indicates that larger dipolar angle can give rise to greater tilt in molecular organization within a layer.

Physics Letters A, 2011

ABSTRACT We propose a soft ellipsoid contact potential model (SECP) for a pair of identical uniax... more ABSTRACT We propose a soft ellipsoid contact potential model (SECP) for a pair of identical uniaxial ellipsoidal molecules, considering the configuration dependent energy anisotropy explicitly along with their geometrical aspects. The present model is an extension of the ellipsoid contact potential (ECP), main contribution of which was to determine the correct contact function of the ellipsoidal core. Expressions for intermolecular forces and torques derived analytically from this new model pair interaction potential are presented hereto to make it useful for molecular dynamics simulation study. We also report on some observations of molecular dynamics simulation study to demonstrate the ability of this realistic coarse-grained potential in generating some important liquid crystal phases.

Physical Review Letters, 2013

The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absenc... more The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long-range positional order is considered as an outstanding problem of great fundamental and technological interest. We report here off-lattice Monte Carlo simulations of a system of polar achiral disklike ellipsoids which spontaneously exhibit a novel ferroelectric nematic phase which is a liquid in three dimensions, considering attractive-repulsive pair interaction suitable for the anisotropic particles. At lower temperature, the ferroelectric nematic phase condenses to a ferroelectric hexagonal columnar fluid with an axial macroscopic polarization. A spontaneous ferroelectric order of dipolar origin is established here for the first time in columnar liquid crystals. Our study demonstrates that simple dipolar interactions are indeed sufficient to produce a class of novel ferroelectric fluids of essential interest. The present work reveals the structure-property relationship of achieving long searched ferroelectric liquid crystal phases and transitions between them, and we hope these findings will help in future development of technologically important fluid ferroelectric materials.

Physical Review E, 2014

In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012)], we have presented t... more In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012)], we have presented the results of a Monte Carlo simulation study of the systems of dipolar Gay-Berne ellipsoids where two terminal antiparallel dipoles are placed symmetrically on the long axis of each ellipsoid, and the results revealed the combined contribution of dipolar separation and transverse orientations in controlling the tilt angle in the tilted hexatic smectic phase. The tilt angle changed from zero to a significant value, in the case of transverse dipoles, with a change in the dipolar separation. In the related comment, Madhusudana [preceding Comment, Phys. Rev. E 89, 046501 (2014)] has claimed that the physical origin of the molecular tilt in the significantly tilted phases found in the simulations is similar to that proposed by McMillan [Phys. Rev. A 8, 1921 (1973)]. Here, we explain that the claim is not correct and make it clear that the two compared pictures are quite different. In the preceding Comment, Madhusudana has also suggested an alternative explanation for tilt generation in the simulations by criticizing the original one proposed by us. We argue here in support of the original explanation and clarify that his explanation does not follow the simulation results.

arXiv (Cornell University), Jan 30, 2020

To understand mechanism of cell-membrane compartmentalization, we studied coarse-grained model sy... more To understand mechanism of cell-membrane compartmentalization, we studied coarse-grained model systems consisting of lipid and cholesterol molecules. Cholesterol plays crucial role in lateral phase segregation in the bilayered lipid membrane to form cholesterol rich liquid ordered domains, termed as 'rafts'. In this NVT Molecular Dynamics simulation study, we have investigated the role of cholesterol in raft-like domain formation. The study reveals that the strength of cholesterol interaction is an important factor behind the phase segregation to form cholesterol rich domains, whereas, the relative dipolar strength of lipid and cholesterol molecules controls the formation of multi-bilayered stack.

arXiv (Cornell University), Dec 3, 2019

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral... more We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

The Journal of Physical Chemistry B

A simple, dual-site model of bolaamphiphiles (bolaforms or bipolar amphiphiles) is developed base... more A simple, dual-site model of bolaamphiphiles (bolaforms or bipolar amphiphiles) is developed based on an earlier single-site model of (monopolar) amphiphiles [S. Dey, J. Saha, Phys. Rev. E 95, 023315 (2017)]. The model incorporates aqueous environment (both hydrophobic effect and hydration force) in its anisotropic site-site interactions, thus obviating the need to simulate solvent particles explicitly. This economy of sites and the absence of explicit solvent particles enable molecular dynamics simulations of bolaamphiphiles to achieve mesoscopic length and timescales unattainable by any bead-spring model or explicit solvent computations. The model applies to generic bolas only, since the gain in scale can only be obtained by sacrificing the resolution of detailed molecular structure. Thanks to dual-sites, however, (as opposed to a singlesite model) our model can incorporate the essential flexibility of bolas that leads to their U-conformers. The model bolas show successful selfassembly into experimentally observed nano-structures like micelles, rods, lamellae etc. and retain fluidity in very stable monolayers. Presence of membrane-spanning model bolas in bilayers of model monopolar amphiphiles increases the stability and impermeability of the lamellar phase. Model bolas are also seen to be less diffusive and to produce thicker layers compared to their monopolar counterparts. Rigid model bolas, though achiral themselves, show self-assembly into helical rods. As all these observations agree with the well-known key characteristics of archaeal lipids and synthetic bolaamphiphiles, our model promises to be effective for studies of bolas in context of biomimetics, drug-delivery and low molecular weight hydrogelators. To the best of our knowledge, no other single or dual-site, solvent-free model for bolas has been reported thus far.

Computationally, low-resolution coarse-grained models provide the most viable means for simulatin... more Computationally, low-resolution coarse-grained models provide the most viable means for simulating the large length and time scales associated with mesoscopic phenomena. Moreover, since lyotropic phases in solution may contain high solvent to amphiphile ratio, implicit solvent models are appropriate for many purposes. By modifying the well-known Gay-Berne potential with an imposed uni-directionality and a longer range, we have come to a simple single-site model amphiphile that can rapidly self-assemble to give diverse lyotropic phases without the explicit incorporation of solvent particles. The model represents a tuneable packing parameter that manifests in the spontaneous curvature of amphiphile aggregates. Apart from large scale simulations (e.g. the study of self-assembly, amphiphile mixing, domain formation etc.) this novel, non-specific model may be useful for suggestive pilot projects with modest computational resources. No such self-assembling, single-site amphiphile model ha...

JCIS Open, 2021

Implicit solvent, coarse-grained models with pairwise interactions can access the largest length ... more Implicit solvent, coarse-grained models with pairwise interactions can access the largest length and time scales in molecular dynamics simulations, owing to the absence of computationally expensive interactions with a huge number of solvent particles, the smaller number of interaction sites in the model molecules, and the lack of fast sub-molecular degrees of freedom. Without an explicit solvent, the solvent mediated effects, e.g. the hydrophobic effect and the hydration force, are mimicked entirely through the interactions between the model molecules. In this paper, we describe a maximally coarse-grained model for lipids in implicit water. The model is called SiMPLISTIC, which is an acronym for 'Single-site Model with Pairwise interaction for Lipids in Implicit Solvent with Tuneable Intrinsic Curvature'. SiMPLISTIC lipids rapidly self-assemble into realistic nonlamellar and lamellar phases such as inverted micelles and bilayers, the spontaneous curvature of the phase being determined by a single free parameter of the model. Model membrane simulations with lamellar SiMPLISTIC lipids show satisfactory fluid and gel phases with no interdigitation or tilt. Despite being rigid molecules, SiMPLISTIC lipids can generate experimentally relevant values for the bending stiffness of model membrane bilayers with no significant interleaflet coupling. SiMPLISTIC can also simulate mixtures of lipids that differ in their packing parameter or length, the latter leading to the phenomenon of hydrophobic mismatch driven phase separation or domain formation. The model has a large scope due to its speed, conceptual and computational simplicity, and versatility. Applications may range from academic and industrial research in various lipid-based systems, such as lyotropic liquid crystals, biological and biomimetic membranes, vectors for drug and gene delivery, emulsions for cosmetic products, to education, such as teaching/learning concepts like self-assembly, polymorphism, biomembrane organization etc. through interactive molecular dynamics simulations.

Fluid Phase Equilibria, 2021

Scientific Reports, 2020

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral... more We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

DAE SOLID STATE PHYSICS SYMPOSIUM 2019, 2020

Physical Review Research, 2019

We report a computer simulation study of the phase transitional behavior of a system of chiral Ga... more We report a computer simulation study of the phase transitional behavior of a system of chiral Gay-Berne molecules embedded with a terminal dipole. In this Rapid Communication, coarse-grained modeling is done to study the influence of coupled chiral and dipolar interactions on the macroscopic liquid crystalline phase behavior. This NV T molecular dynamics simulation study presents the formation of the smectic blue phase (BP Sm), which is a comparatively recent experimentally discovered chiral phase. Our study reveals that a gradual increment of the strength of the chiral interaction brings conventional cholesteric and blue phases, whereas the addition of a dipolar interaction can induce the smectic blue phase. Moreover, we demonstrate that a further increase of dipolar strength makes novel chiral bilayer phases feasible, yet to be realized experimentally.

International Journal of Modern Physics B, 1997

The mean field model for rectangular lattice having herring-bone packing of tilted molecules has ... more The mean field model for rectangular lattice having herring-bone packing of tilted molecules has been extended to reproduce even–odd alternation in the transition temperatures in a discotic system by taking into account the specific change in layering interaction and molecular biaxiality for each member of a homologous series.

Physical Review E, 2017

We report the effect of lipid head-group dipole orientation on phase behaviour of phospholipid as... more We report the effect of lipid head-group dipole orientation on phase behaviour of phospholipid assembly. The work explains molecular-scale mechanism of ion-lipid, anesthetic-lipid interactions where reorientation of dipoles play important role in membrane potential modification. Molecular Dynamics simulations are performed to analyse structure-property relationship and dynamical behaviour of lipid biomembranes considering coarse-grained model interactions.

Physical Review B, 1994

The low value of {T,-T*)/T, =0.1%, where T, is the nematic-isotropic phase-transition temperature... more The low value of {T,-T*)/T, =0.1%, where T, is the nematic-isotropic phase-transition temperature and T is the temperature at which the light-scattering intensity diverges in the supercooled isotropic phase for the nematic-isotropic transition is a long-standing puzzle. We show in this paper that by extending the renormalization-group calculation to second order of c and, alternatively, by considering that the nematic-isotropic transition is close to the tricritical point, considerable improvement over previous results is possible.

Molecular Simulation, 2016

ABSTRACT A soft ellipsoid contact potential model for a pair of biaxial ellipsoidal molecules is ... more ABSTRACT A soft ellipsoid contact potential model for a pair of biaxial ellipsoidal molecules is proposed which considers the configuration dependent energy anisotropy explicitly along with their geometrical aspects. We performed Molecular Dynamics simulation study to generate both biaxial smectic and nematic phases using this new potential.

Physics Letters A, 1992

ABSTRACT A smectic-nematic-isotropic phase transition sequence is reproduced in a 10×10×10 system... more ABSTRACT A smectic-nematic-isotropic phase transition sequence is reproduced in a 10×10×10 system. The pair interaction assumed is purely anisotropic and attractive. Temperature variations of order parameters show qualitatively the same features as those in the McMillan model.

Physical Review E, 2014

The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absenc... more The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.

Physics Letters A, 1997

A site-site potential with a hexagonal distribution of sites with one additional site at the cent... more A site-site potential with a hexagonal distribution of sites with one additional site at the centre, which can simulate disc-like molecules, is presented. To mimic this site-site potential a single-site potential has also been developed for aspherical molecules whose symmetry axis is perpendicular to the molecular plane. This potential can be used to study phases and phase transitions of disc-like liquid crystal molecules in a computationally efficient way.

Physics Letters A, 2005

We perform molecular dynamics simulation for a system of Gay–Berne molecules having two terminal ... more We perform molecular dynamics simulation for a system of Gay–Berne molecules having two terminal dipole moments to generate tilted smectic-C liquid crystal phase. We investigate the effect of dipolar orientation with respect to the long molecular axis on phase behaviour. The study indicates that larger dipolar angle can give rise to greater tilt in molecular organization within a layer.

Physics Letters A, 2011

ABSTRACT We propose a soft ellipsoid contact potential model (SECP) for a pair of identical uniax... more ABSTRACT We propose a soft ellipsoid contact potential model (SECP) for a pair of identical uniaxial ellipsoidal molecules, considering the configuration dependent energy anisotropy explicitly along with their geometrical aspects. The present model is an extension of the ellipsoid contact potential (ECP), main contribution of which was to determine the correct contact function of the ellipsoidal core. Expressions for intermolecular forces and torques derived analytically from this new model pair interaction potential are presented hereto to make it useful for molecular dynamics simulation study. We also report on some observations of molecular dynamics simulation study to demonstrate the ability of this realistic coarse-grained potential in generating some important liquid crystal phases.

Physical Review Letters, 2013

The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absenc... more The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long-range positional order is considered as an outstanding problem of great fundamental and technological interest. We report here off-lattice Monte Carlo simulations of a system of polar achiral disklike ellipsoids which spontaneously exhibit a novel ferroelectric nematic phase which is a liquid in three dimensions, considering attractive-repulsive pair interaction suitable for the anisotropic particles. At lower temperature, the ferroelectric nematic phase condenses to a ferroelectric hexagonal columnar fluid with an axial macroscopic polarization. A spontaneous ferroelectric order of dipolar origin is established here for the first time in columnar liquid crystals. Our study demonstrates that simple dipolar interactions are indeed sufficient to produce a class of novel ferroelectric fluids of essential interest. The present work reveals the structure-property relationship of achieving long searched ferroelectric liquid crystal phases and transitions between them, and we hope these findings will help in future development of technologically important fluid ferroelectric materials.

Physical Review E, 2014

In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012)], we have presented t... more In a recent article [T. K. Bose and J. Saha, Phys. Rev. E 86, 050701 (2012)], we have presented the results of a Monte Carlo simulation study of the systems of dipolar Gay-Berne ellipsoids where two terminal antiparallel dipoles are placed symmetrically on the long axis of each ellipsoid, and the results revealed the combined contribution of dipolar separation and transverse orientations in controlling the tilt angle in the tilted hexatic smectic phase. The tilt angle changed from zero to a significant value, in the case of transverse dipoles, with a change in the dipolar separation. In the related comment, Madhusudana [preceding Comment, Phys. Rev. E 89, 046501 (2014)] has claimed that the physical origin of the molecular tilt in the significantly tilted phases found in the simulations is similar to that proposed by McMillan [Phys. Rev. A 8, 1921 (1973)]. Here, we explain that the claim is not correct and make it clear that the two compared pictures are quite different. In the preceding Comment, Madhusudana has also suggested an alternative explanation for tilt generation in the simulations by criticizing the original one proposed by us. We argue here in support of the original explanation and clarify that his explanation does not follow the simulation results.