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Papers by khagendra baral

Research paper thumbnail of Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

Scientific Reports, 2021

Chalcogenide semiconductors and glasses have many applications in the civil and military fields, ... more Chalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quater...

Research paper thumbnail of Ab Initio Study of Hydrolysis Effects in Single and Ion-Exchanged Alkali Aluminosilicate Glasses

The Journal of Physical Chemistry B, 2020

Hydrolysis in alkali-doped aluminosilicate glasses is one of the most complicated mechanisms in g... more Hydrolysis in alkali-doped aluminosilicate glasses is one of the most complicated mechanisms in glass science. There remain many fundamental and unresolved issues with implications on their potential applications. Herein, we address this challenge by carrying out detailed calculations on the structure and properties of both anhydrate (dry) and hydrated alkali aluminosilicate glasses on carefully constructed models. Specifically, the Na-, (Na + K)- and K-doped aluminosilicate glasses with compositions (SiO2)0.6 (Al2O3)0.2 (Na2O)0.2-x (K2O)x (x = 0, 0.10 and 0.20) are simulated using ab initio molecular dynamics (AIMD). The local short- and intermediate-range order in these glasses are analyzed in terms of atomic pair distribution, coordination number, bond length and bond angle distributions to delineate the subtle variations due to different alkali size and hydrolysis. The electronic structure, interatomic bonding, mechanical and optical properties for these models are calculated and validated with available experimental data. We use the novel concept of total bond order density (TBOD), the quantum mechanically derived metric, to characterize the internal cohesion and strength in the simulated glasses. Detailed analysis of the hydrolysis mechanism enables us to provide information on the complex interplay of various participating elements and their interactions at the atomic level. Such detailed information provides new platform of knowledge which is crucial for understanding the issues related to glass corrosion and durability and ways and means for their special applications in commercial glass products. Both un-dissociated molecular water and dissociated water in the form of hydroxyl group exist in the hydrated models in the presence of alkali ions. For the first time, we observed the opposite mixed alkali effect in the Poisson's ratio for anhydrate and hydrated glasses.

Research paper thumbnail of Solvent Effect on the Structure and Properties of RGD Peptide (1FUV) at Body Temperature (310 K) Using Ab Initio Molecular Dynamics

Polymers, 2021

The structure and properties of the arginine-glycine-aspartate (RGD) sequence of the 1FUV peptide... more The structure and properties of the arginine-glycine-aspartate (RGD) sequence of the 1FUV peptide at 0 K and body temperature (310 K) are systematically investigated in a dry and aqueous environment using more accurate ab initio molecular dynamics and density functional theory calculations. The fundamental properties, such as electronic structure, interatomic bonding, partial charge distribution, and dielectric response function at 0 and 310 K are analyzed, comparing them in dry and solvated models. These accurate microscopic parameters determined from highly reliable quantum mechanical calculations are useful to define the range and strength of complex molecular interactions occurring between the RGD peptide and the integrin receptor. The in-depth bonding picture analyzed using a novel quantum mechanical metric, the total bond order (TBO), quantifies the role played by hydrogen bonds in the internal cohesion of the simulated structures. The TBO at 310 K decreases in the dry model b...

Research paper thumbnail of Temperature-Dependent Properties of Molten Li2BeF4 Salt Using Ab Initio Molecular Dynamics

ACS Omega

Molten lithium tetrafluoroberyllate (Li 2 BeF 4) salt, also known as FLiBe, with a 2:1 mixture of... more Molten lithium tetrafluoroberyllate (Li 2 BeF 4) salt, also known as FLiBe, with a 2:1 mixture of LiF and BeF 2 is being proposed as a coolant and solvent in advanced nuclear reactor designs, such as the molten salt reactor or the fluoride salt cooled high-temperature reactor. We present the results on the structure and properties of FLiBe over a wide range of temperatures, 0−2000 K, from high-throughput ab initio molecular dynamics simulation using a supercell model of 504 atoms. The variations in the local structures of solid and liquid FLiBe with temperature are discussed in terms of a pair distribution function, coordination number, and bond angle distribution. The temperature-dependent electronic structure and optical and mechanical properties of FLiBe are calculated. The optical and mechanical property results are reported for the first time. The results above and below the melting temperature (∼732 K) are compared with the experimental data and with data for crystalline FLiBe. The electronic structure and interatomic bonding results are discussed in correlation with the mechanical strength. A novel concept of total bond order density (TBOD), an important quantum mechanical parameter, is used to characterize the internal cohesion and strength in the simulated models. The results show a variation in the rate of change in properties in solid and liquid phases with anomalous behavior across the melting region. The observed trend is the decrease in mechanical strength, band gap, and TBOD in a nonlinear fashion as a function of temperature. The refractive index shows a surprising minimum at 850 K, among the tested temperatures, which lies above the melting point. These findings provide a new platform to understand the interplay between the temperature-dependent structures and properties of FLiBe salt.

Research paper thumbnail of Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

Scientific Reports

Chalcogenide semiconductors and glasses have many applications in the civil and military fields, ... more Chalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quater...

Research paper thumbnail of Conspicuous interatomic bonding in chalcogenide crystals and implications on electronic, optical, and elastic properties

AIP Advances

Chalcogenide crystals are a unique class of materials very different from semiconductors or metal... more Chalcogenide crystals are a unique class of materials very different from semiconductors or metallic alloys. They also have many practical applications, especially in relation to their optical properties. However, the fundamental understanding of their electronic structure and physical properties is rather scattered and incomplete. We present a detailed study using first-principles calculations on the electronic structure, interatomic bonding, and optical and mechanical properties for 32 chalcogenide crystals. They consist of 22 binary (AnBm) and 10 ternary (AnA ′ Bm) crystals with A =

Research paper thumbnail of Interfacial interaction between Suolunite Crystal and Silica Binding Peptide for Novel Bio-inspired Cement

ACS Combinatorial Science

Research paper thumbnail of Ab initio molecular dynamics simulation of Na-doped aluminosilicate glasses and glass-water interaction

AIP Advances

The structure and properties of sodium aluminosilicate (NAS) glasses are investigated using ab in... more The structure and properties of sodium aluminosilicate (NAS) glasses are investigated using ab initio molecular dynamics and density functional calculations. Four NAS glass models of about 700 atoms with composition (SiO 2) 0.6 (Al 2 O 3) 0.4-x (Na 2 O)x with Na/Al ratio R = 0.0, 0.5, 1.0 and 1.5 are constructed corresponding to x = 0, 0.135, 0.20 and 0.24. Detailed information on network coordination, electronic structure, interatomic bonding and partial charge distribution, mechanical and optical properties of these models are presented and fully analyzed. The structural details for each R are discussed in terms of short-and intermediate-range order manifested in the coordination number, atomic pair and bond angle distributions. It is shown that the mechanical strength of NAS glasses decreases with increasing Na content, indicating that pure aluminosilicate glass is stronger than the alkali-doped glasses. We use the novel concept of total bond order density to characterize the internal cohesion of the NAS glasses. In the case of R = 1 NAS model, 12 water molecules are added to investigate the solvation effect and hydrolysis in NAS glass.

Research paper thumbnail of Total Bond Order Density as a Quantum Mechanical Metric for Materials Design: Application to Chalcogenide Crystals

Materials design for processing and application requires fundamental understanding of their prope... more Materials design for processing and application requires fundamental understanding of their properties based interatomic interaction. The use of the novel concept of total bond order density (TBOD) as a single quantum mechanical metric to characterize the internal cohesion of a crystal and correlate with the calculated physical properties is particularly appealing. This requires detailed first-principles calculation of the electronic structure, interatomic bonding and related properties. In this article, we use this new concept and apply it to chalcogenide crystals based on data obtained from 25 crystals: Ag2S, Ag2Se, Ag2Te, As2S3, As2Se3, As2Te3, As4Se4, Cu2S, Cu2Se, Cu2Te, Cu4GeS4, Cu2SnS3, Cu2SnSe3, GeS2, GeSe2, Ge4Se9, Sb2S3, Sb2Se3, Sb2Te3, SnS, SnSe, CdSe, CdTe, ZnSe, and ZnTe. Together with the calculated optical and mechanical properties, we demonstrate the efficacy of using this novel approach for materials design that could facilitate the exploration and development of new...

Research paper thumbnail of Understanding the atomistic origin of hydration effects in single and mixed bulk alkali-silicate glasses

Journal of the American Ceramic Society

Silica-water interaction plays an essential role for the mechanical strength and chemical durabil... more Silica-water interaction plays an essential role for the mechanical strength and chemical durability of alkali-doped-silicate glasses. A comprehensive study of single and mixed alkali-silicate glasses with 30% molar content of Li 2 O, Na 2 O, and K 2 O, and half-half mixture of Li 2 O-Na 2 O, Li 2 O-K 2 O, and Na 2 O-K 2 O in hydrated models is carried out using density functional theory methods. Information on atomic geometry, electronic structure, interatomic bonding, partial charge distribution, mechanical, and optical properties are obtained and compared. It confirms that water in the solvated and confined bulk models can be either dissociated or remains as H 2 O molecule depending on the distribution and specific alkali elements. A quantum mechanical metric, the total bond order density is used to unravel the atomistic origin of the internal cohesion and strength of glasses in different environments. In particular, we show that the mechanical strength of bulk alkali-silicate glasses is enhanced by hydration with some evidence that mixing of alkali ions tends to degrade the strength of the hydrated glasses. These results are discussed in the context of experimental observations and a few existing simulations using classical molecular dynamics.

Research paper thumbnail of Ab initioModeling of the Electronic Structures and Physical Properties of a-Si1−xGexO2Glass (x= 0 to 1)

Journal of the American Ceramic Society, 2016

Research paper thumbnail of Main-chain polyoxometalate-containing donor–acceptor conjugated copolymers: synthesis, characterization, morphological studies and applications in single-component photovoltaic cells

RSC Adv., 2016

Single-component solar cells of main-chain polyoxometalate-containing donor–acceptor conjugated c... more Single-component solar cells of main-chain polyoxometalate-containing donor–acceptor conjugated copolymers show efficiencies comparable to those conjugated polymers with covalently bonded fullerenes.

Research paper thumbnail of Ab Initio Modeling of Structure and Properties of Single and Mixed Alkali Silicate Glasses

The Journal of Physical Chemistry A

Research paper thumbnail of Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

Scientific Reports, 2021

Chalcogenide semiconductors and glasses have many applications in the civil and military fields, ... more Chalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quater...

Research paper thumbnail of Ab Initio Study of Hydrolysis Effects in Single and Ion-Exchanged Alkali Aluminosilicate Glasses

The Journal of Physical Chemistry B, 2020

Hydrolysis in alkali-doped aluminosilicate glasses is one of the most complicated mechanisms in g... more Hydrolysis in alkali-doped aluminosilicate glasses is one of the most complicated mechanisms in glass science. There remain many fundamental and unresolved issues with implications on their potential applications. Herein, we address this challenge by carrying out detailed calculations on the structure and properties of both anhydrate (dry) and hydrated alkali aluminosilicate glasses on carefully constructed models. Specifically, the Na-, (Na + K)- and K-doped aluminosilicate glasses with compositions (SiO2)0.6 (Al2O3)0.2 (Na2O)0.2-x (K2O)x (x = 0, 0.10 and 0.20) are simulated using ab initio molecular dynamics (AIMD). The local short- and intermediate-range order in these glasses are analyzed in terms of atomic pair distribution, coordination number, bond length and bond angle distributions to delineate the subtle variations due to different alkali size and hydrolysis. The electronic structure, interatomic bonding, mechanical and optical properties for these models are calculated and validated with available experimental data. We use the novel concept of total bond order density (TBOD), the quantum mechanically derived metric, to characterize the internal cohesion and strength in the simulated glasses. Detailed analysis of the hydrolysis mechanism enables us to provide information on the complex interplay of various participating elements and their interactions at the atomic level. Such detailed information provides new platform of knowledge which is crucial for understanding the issues related to glass corrosion and durability and ways and means for their special applications in commercial glass products. Both un-dissociated molecular water and dissociated water in the form of hydroxyl group exist in the hydrated models in the presence of alkali ions. For the first time, we observed the opposite mixed alkali effect in the Poisson's ratio for anhydrate and hydrated glasses.

Research paper thumbnail of Solvent Effect on the Structure and Properties of RGD Peptide (1FUV) at Body Temperature (310 K) Using Ab Initio Molecular Dynamics

Polymers, 2021

The structure and properties of the arginine-glycine-aspartate (RGD) sequence of the 1FUV peptide... more The structure and properties of the arginine-glycine-aspartate (RGD) sequence of the 1FUV peptide at 0 K and body temperature (310 K) are systematically investigated in a dry and aqueous environment using more accurate ab initio molecular dynamics and density functional theory calculations. The fundamental properties, such as electronic structure, interatomic bonding, partial charge distribution, and dielectric response function at 0 and 310 K are analyzed, comparing them in dry and solvated models. These accurate microscopic parameters determined from highly reliable quantum mechanical calculations are useful to define the range and strength of complex molecular interactions occurring between the RGD peptide and the integrin receptor. The in-depth bonding picture analyzed using a novel quantum mechanical metric, the total bond order (TBO), quantifies the role played by hydrogen bonds in the internal cohesion of the simulated structures. The TBO at 310 K decreases in the dry model b...

Research paper thumbnail of Temperature-Dependent Properties of Molten Li2BeF4 Salt Using Ab Initio Molecular Dynamics

ACS Omega

Molten lithium tetrafluoroberyllate (Li 2 BeF 4) salt, also known as FLiBe, with a 2:1 mixture of... more Molten lithium tetrafluoroberyllate (Li 2 BeF 4) salt, also known as FLiBe, with a 2:1 mixture of LiF and BeF 2 is being proposed as a coolant and solvent in advanced nuclear reactor designs, such as the molten salt reactor or the fluoride salt cooled high-temperature reactor. We present the results on the structure and properties of FLiBe over a wide range of temperatures, 0−2000 K, from high-throughput ab initio molecular dynamics simulation using a supercell model of 504 atoms. The variations in the local structures of solid and liquid FLiBe with temperature are discussed in terms of a pair distribution function, coordination number, and bond angle distribution. The temperature-dependent electronic structure and optical and mechanical properties of FLiBe are calculated. The optical and mechanical property results are reported for the first time. The results above and below the melting temperature (∼732 K) are compared with the experimental data and with data for crystalline FLiBe. The electronic structure and interatomic bonding results are discussed in correlation with the mechanical strength. A novel concept of total bond order density (TBOD), an important quantum mechanical parameter, is used to characterize the internal cohesion and strength in the simulated models. The results show a variation in the rate of change in properties in solid and liquid phases with anomalous behavior across the melting region. The observed trend is the decrease in mechanical strength, band gap, and TBOD in a nonlinear fashion as a function of temperature. The refractive index shows a surprising minimum at 850 K, among the tested temperatures, which lies above the melting point. These findings provide a new platform to understand the interplay between the temperature-dependent structures and properties of FLiBe salt.

Research paper thumbnail of Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

Scientific Reports

Chalcogenide semiconductors and glasses have many applications in the civil and military fields, ... more Chalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quater...

Research paper thumbnail of Conspicuous interatomic bonding in chalcogenide crystals and implications on electronic, optical, and elastic properties

AIP Advances

Chalcogenide crystals are a unique class of materials very different from semiconductors or metal... more Chalcogenide crystals are a unique class of materials very different from semiconductors or metallic alloys. They also have many practical applications, especially in relation to their optical properties. However, the fundamental understanding of their electronic structure and physical properties is rather scattered and incomplete. We present a detailed study using first-principles calculations on the electronic structure, interatomic bonding, and optical and mechanical properties for 32 chalcogenide crystals. They consist of 22 binary (AnBm) and 10 ternary (AnA ′ Bm) crystals with A =

Research paper thumbnail of Interfacial interaction between Suolunite Crystal and Silica Binding Peptide for Novel Bio-inspired Cement

ACS Combinatorial Science

Research paper thumbnail of Ab initio molecular dynamics simulation of Na-doped aluminosilicate glasses and glass-water interaction

AIP Advances

The structure and properties of sodium aluminosilicate (NAS) glasses are investigated using ab in... more The structure and properties of sodium aluminosilicate (NAS) glasses are investigated using ab initio molecular dynamics and density functional calculations. Four NAS glass models of about 700 atoms with composition (SiO 2) 0.6 (Al 2 O 3) 0.4-x (Na 2 O)x with Na/Al ratio R = 0.0, 0.5, 1.0 and 1.5 are constructed corresponding to x = 0, 0.135, 0.20 and 0.24. Detailed information on network coordination, electronic structure, interatomic bonding and partial charge distribution, mechanical and optical properties of these models are presented and fully analyzed. The structural details for each R are discussed in terms of short-and intermediate-range order manifested in the coordination number, atomic pair and bond angle distributions. It is shown that the mechanical strength of NAS glasses decreases with increasing Na content, indicating that pure aluminosilicate glass is stronger than the alkali-doped glasses. We use the novel concept of total bond order density to characterize the internal cohesion of the NAS glasses. In the case of R = 1 NAS model, 12 water molecules are added to investigate the solvation effect and hydrolysis in NAS glass.

Research paper thumbnail of Total Bond Order Density as a Quantum Mechanical Metric for Materials Design: Application to Chalcogenide Crystals

Materials design for processing and application requires fundamental understanding of their prope... more Materials design for processing and application requires fundamental understanding of their properties based interatomic interaction. The use of the novel concept of total bond order density (TBOD) as a single quantum mechanical metric to characterize the internal cohesion of a crystal and correlate with the calculated physical properties is particularly appealing. This requires detailed first-principles calculation of the electronic structure, interatomic bonding and related properties. In this article, we use this new concept and apply it to chalcogenide crystals based on data obtained from 25 crystals: Ag2S, Ag2Se, Ag2Te, As2S3, As2Se3, As2Te3, As4Se4, Cu2S, Cu2Se, Cu2Te, Cu4GeS4, Cu2SnS3, Cu2SnSe3, GeS2, GeSe2, Ge4Se9, Sb2S3, Sb2Se3, Sb2Te3, SnS, SnSe, CdSe, CdTe, ZnSe, and ZnTe. Together with the calculated optical and mechanical properties, we demonstrate the efficacy of using this novel approach for materials design that could facilitate the exploration and development of new...

Research paper thumbnail of Understanding the atomistic origin of hydration effects in single and mixed bulk alkali-silicate glasses

Journal of the American Ceramic Society

Silica-water interaction plays an essential role for the mechanical strength and chemical durabil... more Silica-water interaction plays an essential role for the mechanical strength and chemical durability of alkali-doped-silicate glasses. A comprehensive study of single and mixed alkali-silicate glasses with 30% molar content of Li 2 O, Na 2 O, and K 2 O, and half-half mixture of Li 2 O-Na 2 O, Li 2 O-K 2 O, and Na 2 O-K 2 O in hydrated models is carried out using density functional theory methods. Information on atomic geometry, electronic structure, interatomic bonding, partial charge distribution, mechanical, and optical properties are obtained and compared. It confirms that water in the solvated and confined bulk models can be either dissociated or remains as H 2 O molecule depending on the distribution and specific alkali elements. A quantum mechanical metric, the total bond order density is used to unravel the atomistic origin of the internal cohesion and strength of glasses in different environments. In particular, we show that the mechanical strength of bulk alkali-silicate glasses is enhanced by hydration with some evidence that mixing of alkali ions tends to degrade the strength of the hydrated glasses. These results are discussed in the context of experimental observations and a few existing simulations using classical molecular dynamics.

Research paper thumbnail of Ab initioModeling of the Electronic Structures and Physical Properties of a-Si1−xGexO2Glass (x= 0 to 1)

Journal of the American Ceramic Society, 2016

Research paper thumbnail of Main-chain polyoxometalate-containing donor–acceptor conjugated copolymers: synthesis, characterization, morphological studies and applications in single-component photovoltaic cells

RSC Adv., 2016

Single-component solar cells of main-chain polyoxometalate-containing donor–acceptor conjugated c... more Single-component solar cells of main-chain polyoxometalate-containing donor–acceptor conjugated copolymers show efficiencies comparable to those conjugated polymers with covalently bonded fullerenes.

Research paper thumbnail of Ab Initio Modeling of Structure and Properties of Single and Mixed Alkali Silicate Glasses

The Journal of Physical Chemistry A