Sandeep Kumar Jain - Academia.edu (original) (raw)

Papers by Sandeep Kumar Jain

Applied Nanoscience, 2012

AIP Advances, 2016

Ab initio calculations on hard/soft (FePt) m /(FeCo) n , (m = 4, 6, 8 and n = 2-2m) magnetic supe... more Ab initio calculations on hard/soft (FePt) m /(FeCo) n , (m = 4, 6, 8 and n = 2-2m) magnetic superlattices show that the B2 type FeCo layers become anisotropic with varying interlayer spacing and enhanced magnetic moments. The average magnetic moment in superlattices is higher than in bulk FePt, resulting in high maximum energy product for (FePt) 4 /(FeCo) 8 which is nearly double the calculated value for bulk FePt. The calculation of the magnetic anisotropy energy shows that the optimal thickness of the soft magnetic phase for good permanent magnet behaviour of the superlattice is less than ∼2 nm.

IOP Conference Series: Materials Science and Engineering, 2015

Advanced Materials Research, 2011

International Journal of Advanced Intelligence Paradigms, 2013

Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density fu... more Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density functional theory (DFT) and pseudo-potentials, the minimisation of potential energy and relative stability for Ni n clusters (n = 2 -22) were studied. The genetic algorithm (GA), differential evaluation (DE), particle swarm optimisation (PSO) and artificial bee colony (ABC) are used for global structural optimisations with space-fixed Cartesian coordinates. Clusters obtained from NIA search were further optimised by using first principals total energy calculations. We found that GA gives minimum energy for Ni n (n = 6, 11, 16, 21), DE gives minimum energy for Ni n (n = 2, 4, 7, 9, 15, 17), PSO gives minimum energy for Ni n (n = 3, 10, 12, 14, 18, 20) and ABC gives minimum energy for Ni n (n = 5, 8, 13, 19, 22).

Ab initio calculations have been performed for determining structural stabilities of nitrogen-dop... more Ab initio calculations have been performed for determining structural stabilities of nitrogen-doped ultrathin single-walled boron nanotube. We have considered ultrathin boron nanotubes of diameters \0.5 nm, which include mainly three conformations of BNTs viz. zigzag (5,0), armchair (3,3) and chiral (4,2) with diameters 4.60, 4.78 and 4.87 Å , respectively. It has been investigated that a-BNTs are highly stable, while hexagonal BNTs are found to be least stable. In view of increasing structural stability of hexagonal BNTs, substitutional doping of foreign atoms, i.e. nitrogen is chosen. The nitrogen atoms substitute the host atoms at the middle of the tubes. The substitution doping is made with all the three conformations. The structural stabilities of BNTs have been investigated by using density functional theory (DFT). Subsequently, the cohesive energy is calculated, which directly measures the structural stability. The cohesive energy of BNTs has been calculated for different nitrogen concentrations. We found that the structures get energetically more stable with increasing nitrogen concentration. Moreover, it is also revealed that all the three BNTs are almost equally stable for single-atom doping, while the armchair BNT (3,3) is highly stable followed by zigzag (5,0) and chiral (4,2) BNTs for two-and three-atom doping. The structural stability is an important factor for realization of any physical device. Thus, these BNTs can be used for field emission, semiconducting and highly conducting devices at nanoscale.

The European Physical Journal B, 2013

ABSTRACT We report dielectric function related optical properties namely dielectric constant, sta... more ABSTRACT We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant ɛ1(ω) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

The European Physical Journal B, 2013

ABSTRACT The pseudopotential calculations have been performed to study the effect of carbon impur... more ABSTRACT The pseudopotential calculations have been performed to study the effect of carbon impurity on the electronic nature of hexagonal ultrathin boron nanotubes. The structural stability and electronic properties of C-substituted BNTs have been evaluated by first principles calculations. Three conformations of BNTs viz. armchair (3,3), zigzag (5,0), and chiral (4,2), have been considered for examining the effects of carbon substitution. It is observed that carbon substituted hexagonal ultrathin BNTs become energetically more stable in contrast to pristine ones. It is revealed that all the C-substituted hexagonal BNTs are metallic and independent of chirality & impurity concentration. Thus, the chirality of C-substituted BNTs is controlled to a certain extent. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

Condensed Matter Physics, 2013

ABSTRACT An ab initio calculations have been carried out for examining the curvature effect of sm... more ABSTRACT An ab initio calculations have been carried out for examining the curvature effect of small diameter hexagonal boron nanotubes. The considered conformations of boron nanotubes are namely armchair (3,3), zigzag (5,0), and chiral (4,2) and consisting 12, 20,and 56 atoms respectively. The strain energy is evaluated in order to examine the curvature effect. It is found that the strain energy of hexagonal BNT strongly depends upon radius. Whereas the strain energy of triangular BNTs depends on both radius and chirality.

Journal of Applied Physics, 2013

ABSTRACT We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes ... more ABSTRACT We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes of incident light in the framework of density functional theory. We have considered three models of small diameter (below 5 Å) BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) consisting 12, 20, and 56 atoms, respectively. In this convolution, we have investigated various optical parameters such as static dielectric constant, plasma frequency, absorption coefficient, refractive index, reflectivity, and optical conductivity for unpolarized [100], parallel polarized [001], and perpendicular polarized light [100]. The parallel and perpendicular polarized lights ensure the anisotropic nature of BNTs. The study reveals the highest static dielectric constants for chiral BNTs correspond to parallel polarized and unpolarized light, indicating good dielectric materials. The highest absorption coefficient is reported for armchair (3,3) BNT among all the considered models. Moreover, small absorption is noticed in comparison to CNTs. The small electron energy loss is obtained for parallel polarized light in contrast to perpendicular ones. The static refractive index follows the same trend as that of static dielectric constant, i.e., (4,2)>(3,3)>(5,0) for unpolarized and parallel polarized lights. Whereas, for perpendicular polarized light, they exhibit different order, i.e., (3,3)>(5,0)>(4,2). However, the static and maximum refractive indices are obtained high for chiral (4,2) BNT correspond to parallel polarized light. Further, the reflectivity and conductivity of (3,3) BNT bring out to be the highest for all the incident light. The high conductivity is predicted for armchair and chiral BNTs correspond to parallel polarized light. These predictions proved to be promising candidate for field emission and opto-electronic devices. The present calculated findings are well compared with the available experimental and theoretical results of other nanotubes.

The European Physical Journal B, 2014

Advances in Condensed Matter Physics, 2014

For the first time we present electronic band structure and density of states for nitrogen doped ... more For the first time we present electronic band structure and density of states for nitrogen doped hexagonal ultrathin boron nanotubes in the framework of density functional theory. The considered models of nanotubes below 5Å diameter are armchair (3,3), zigzag (5,0), and chiral (4,2). The impurity chosen for the study is nitrogen and concentration of impurity atoms is limited to two. The study reveals that (3,3) BNT retains its metallic nature after nitrogen doping. However, metallicity gets increased which is attributed by the excess electrons of nitrogen. Further, it also brings out that (5,0) BNT which is originally metal transforms into semiconductor after nitrogen interaction and the band gap at G point increases with the impurity. Moreover, the band gap of (4,2) BNT reduces significantly and turns into semimetal for nitrogen doping. Thus, the nitrogen impurity has the predominant effect on the electronic properties of BNTs and therefore can be regarded as suitable candidates for nanoelectronic and field emission devices.

Computational Materials Science, 2011

We have employed density functional theory calculations in generalized-gradient approximation to ... more We have employed density functional theory calculations in generalized-gradient approximation to investigate electronic and optical properties of single walled boron nanotubes. We have calculated binding energy per atom, band structure, partial density of states, dielectric function, absorption spectra and loss function for armchair (3, 3), zigzag (5, 0) and chiral (4, 2) nanotubes. Our calculations show that (4, 2) nanotube is highly stable and semiconducting with direct band gap of 0.40 eV followed by armchair (3, 3) and zigzag (5, 0) nanotubes depicting metallic nature. The optical properties of periodic nanotubes were performed for parallel and perpendicular polarized light. It is found that all the three nanotubes are anisotropic in nature and chiral (4, 2) nanotube showing single peak for both absorption spectra as well as loss function irrespective of polarization direction.

American Institute of Physics …, 2011

We have employed density functional theory calculations for absorption spectra of copper doped si... more We have employed density functional theory calculations for absorption spectra of copper doped single walled boron nanotube. We have taken zigzag (5,0) single walled boron nanotube with substituting one boron atom by copper (Cu) atom. The nanotube structure contains one atom of copper and 19 atoms of boron. The absorption is determined for parallel and perpendicular polarized light. The absorption is found minimum at higher energy and higher at lower energy under perpendicular polarization. However, the absorption is found higher at higher energy and lower at lower energy under parallel polarization. Thus, the maximum absorption is found for parallel polarized light.

Applied Nanoscience, 2012

AIP Advances, 2016

Ab initio calculations on hard/soft (FePt) m /(FeCo) n , (m = 4, 6, 8 and n = 2-2m) magnetic supe... more Ab initio calculations on hard/soft (FePt) m /(FeCo) n , (m = 4, 6, 8 and n = 2-2m) magnetic superlattices show that the B2 type FeCo layers become anisotropic with varying interlayer spacing and enhanced magnetic moments. The average magnetic moment in superlattices is higher than in bulk FePt, resulting in high maximum energy product for (FePt) 4 /(FeCo) 8 which is nearly double the calculated value for bulk FePt. The calculation of the magnetic anisotropy energy shows that the optimal thickness of the soft magnetic phase for good permanent magnet behaviour of the superlattice is less than ∼2 nm.

IOP Conference Series: Materials Science and Engineering, 2015

Advanced Materials Research, 2011

International Journal of Advanced Intelligence Paradigms, 2013

Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density fu... more Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density functional theory (DFT) and pseudo-potentials, the minimisation of potential energy and relative stability for Ni n clusters (n = 2 -22) were studied. The genetic algorithm (GA), differential evaluation (DE), particle swarm optimisation (PSO) and artificial bee colony (ABC) are used for global structural optimisations with space-fixed Cartesian coordinates. Clusters obtained from NIA search were further optimised by using first principals total energy calculations. We found that GA gives minimum energy for Ni n (n = 6, 11, 16, 21), DE gives minimum energy for Ni n (n = 2, 4, 7, 9, 15, 17), PSO gives minimum energy for Ni n (n = 3, 10, 12, 14, 18, 20) and ABC gives minimum energy for Ni n (n = 5, 8, 13, 19, 22).

Ab initio calculations have been performed for determining structural stabilities of nitrogen-dop... more Ab initio calculations have been performed for determining structural stabilities of nitrogen-doped ultrathin single-walled boron nanotube. We have considered ultrathin boron nanotubes of diameters \0.5 nm, which include mainly three conformations of BNTs viz. zigzag (5,0), armchair (3,3) and chiral (4,2) with diameters 4.60, 4.78 and 4.87 Å , respectively. It has been investigated that a-BNTs are highly stable, while hexagonal BNTs are found to be least stable. In view of increasing structural stability of hexagonal BNTs, substitutional doping of foreign atoms, i.e. nitrogen is chosen. The nitrogen atoms substitute the host atoms at the middle of the tubes. The substitution doping is made with all the three conformations. The structural stabilities of BNTs have been investigated by using density functional theory (DFT). Subsequently, the cohesive energy is calculated, which directly measures the structural stability. The cohesive energy of BNTs has been calculated for different nitrogen concentrations. We found that the structures get energetically more stable with increasing nitrogen concentration. Moreover, it is also revealed that all the three BNTs are almost equally stable for single-atom doping, while the armchair BNT (3,3) is highly stable followed by zigzag (5,0) and chiral (4,2) BNTs for two-and three-atom doping. The structural stability is an important factor for realization of any physical device. Thus, these BNTs can be used for field emission, semiconducting and highly conducting devices at nanoscale.

The European Physical Journal B, 2013

ABSTRACT We report dielectric function related optical properties namely dielectric constant, sta... more ABSTRACT We report dielectric function related optical properties namely dielectric constant, static dielectric constant, and absorption coefficients of C-substituted hexagonal boron nanotubes. The optical properties were computed for parallel and perpendicular polarized light in the framework of density functional theory. In this regard, three models of BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) have been undertaken for probing the effect of carbon impurity. Our calculations show high dielectric constant of armchair and chiral BNTs for parallel polarized light and magnitude becomes smaller for higher impurity concentration, while zigzag BNT exhibits reverse trend for high impurity concentration. For perpendicular polarized light, the magnitude of dielectric constant ɛ1(ω) is decreased and shifts at higher frequencies. The absorption is revealed highest for armchair followed by zigzag and chiral BNTs independent of impurity concentration. The intensity of absorption gets weaken for higher concentration. The chiral BNTs show smaller but uniform absorption in smaller frequency range results in uniform field emission. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

The European Physical Journal B, 2013

ABSTRACT The pseudopotential calculations have been performed to study the effect of carbon impur... more ABSTRACT The pseudopotential calculations have been performed to study the effect of carbon impurity on the electronic nature of hexagonal ultrathin boron nanotubes. The structural stability and electronic properties of C-substituted BNTs have been evaluated by first principles calculations. Three conformations of BNTs viz. armchair (3,3), zigzag (5,0), and chiral (4,2), have been considered for examining the effects of carbon substitution. It is observed that carbon substituted hexagonal ultrathin BNTs become energetically more stable in contrast to pristine ones. It is revealed that all the C-substituted hexagonal BNTs are metallic and independent of chirality & impurity concentration. Thus, the chirality of C-substituted BNTs is controlled to a certain extent. These findings are also compared with available experimental and theoretical results. These metallic nanotubes are promising candidate as interconnects for nanodevices as well as field emission devices.

Condensed Matter Physics, 2013

ABSTRACT An ab initio calculations have been carried out for examining the curvature effect of sm... more ABSTRACT An ab initio calculations have been carried out for examining the curvature effect of small diameter hexagonal boron nanotubes. The considered conformations of boron nanotubes are namely armchair (3,3), zigzag (5,0), and chiral (4,2) and consisting 12, 20,and 56 atoms respectively. The strain energy is evaluated in order to examine the curvature effect. It is found that the strain energy of hexagonal BNT strongly depends upon radius. Whereas the strain energy of triangular BNTs depends on both radius and chirality.

Journal of Applied Physics, 2013

ABSTRACT We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes ... more ABSTRACT We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes of incident light in the framework of density functional theory. We have considered three models of small diameter (below 5 Å) BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) consisting 12, 20, and 56 atoms, respectively. In this convolution, we have investigated various optical parameters such as static dielectric constant, plasma frequency, absorption coefficient, refractive index, reflectivity, and optical conductivity for unpolarized [100], parallel polarized [001], and perpendicular polarized light [100]. The parallel and perpendicular polarized lights ensure the anisotropic nature of BNTs. The study reveals the highest static dielectric constants for chiral BNTs correspond to parallel polarized and unpolarized light, indicating good dielectric materials. The highest absorption coefficient is reported for armchair (3,3) BNT among all the considered models. Moreover, small absorption is noticed in comparison to CNTs. The small electron energy loss is obtained for parallel polarized light in contrast to perpendicular ones. The static refractive index follows the same trend as that of static dielectric constant, i.e., (4,2)>(3,3)>(5,0) for unpolarized and parallel polarized lights. Whereas, for perpendicular polarized light, they exhibit different order, i.e., (3,3)>(5,0)>(4,2). However, the static and maximum refractive indices are obtained high for chiral (4,2) BNT correspond to parallel polarized light. Further, the reflectivity and conductivity of (3,3) BNT bring out to be the highest for all the incident light. The high conductivity is predicted for armchair and chiral BNTs correspond to parallel polarized light. These predictions proved to be promising candidate for field emission and opto-electronic devices. The present calculated findings are well compared with the available experimental and theoretical results of other nanotubes.

The European Physical Journal B, 2014

Advances in Condensed Matter Physics, 2014

For the first time we present electronic band structure and density of states for nitrogen doped ... more For the first time we present electronic band structure and density of states for nitrogen doped hexagonal ultrathin boron nanotubes in the framework of density functional theory. The considered models of nanotubes below 5Å diameter are armchair (3,3), zigzag (5,0), and chiral (4,2). The impurity chosen for the study is nitrogen and concentration of impurity atoms is limited to two. The study reveals that (3,3) BNT retains its metallic nature after nitrogen doping. However, metallicity gets increased which is attributed by the excess electrons of nitrogen. Further, it also brings out that (5,0) BNT which is originally metal transforms into semiconductor after nitrogen interaction and the band gap at G point increases with the impurity. Moreover, the band gap of (4,2) BNT reduces significantly and turns into semimetal for nitrogen doping. Thus, the nitrogen impurity has the predominant effect on the electronic properties of BNTs and therefore can be regarded as suitable candidates for nanoelectronic and field emission devices.

Computational Materials Science, 2011

We have employed density functional theory calculations in generalized-gradient approximation to ... more We have employed density functional theory calculations in generalized-gradient approximation to investigate electronic and optical properties of single walled boron nanotubes. We have calculated binding energy per atom, band structure, partial density of states, dielectric function, absorption spectra and loss function for armchair (3, 3), zigzag (5, 0) and chiral (4, 2) nanotubes. Our calculations show that (4, 2) nanotube is highly stable and semiconducting with direct band gap of 0.40 eV followed by armchair (3, 3) and zigzag (5, 0) nanotubes depicting metallic nature. The optical properties of periodic nanotubes were performed for parallel and perpendicular polarized light. It is found that all the three nanotubes are anisotropic in nature and chiral (4, 2) nanotube showing single peak for both absorption spectra as well as loss function irrespective of polarization direction.

American Institute of Physics …, 2011

We have employed density functional theory calculations for absorption spectra of copper doped si... more We have employed density functional theory calculations for absorption spectra of copper doped single walled boron nanotube. We have taken zigzag (5,0) single walled boron nanotube with substituting one boron atom by copper (Cu) atom. The nanotube structure contains one atom of copper and 19 atoms of boron. The absorption is determined for parallel and perpendicular polarized light. The absorption is found minimum at higher energy and higher at lower energy under perpendicular polarization. However, the absorption is found higher at higher energy and lower at lower energy under parallel polarization. Thus, the maximum absorption is found for parallel polarized light.