Ahmad Nazrul Rosli | Universiti Sains Islam Malaysia (USIM) (original) (raw)

Papers by Ahmad Nazrul Rosli

Research paper thumbnail of DFT Calculation of Vibrations in the Clusters of Zinc and Oxygen Atoms (Pengiraan Getaran bagi Kluster Atom Zink dan Oksigen dengan DFT

The nanometer size clusters are often present in ZnO. We have calculated the vibrational frequenc... more The nanometer size clusters are often present in ZnO. We have calculated the vibrational frequencies of zinc oxide by using the density-functional theory. We synthesized clusters of ZnO starting with ZnO n and continue with Zn 2 O n , Zn 3 O n and Zn 4 O n with n = 1, 2, 3 and 4. By minimizing the energy of the Schrödinger equation, we found the bond lengths and the vibrational frequencies of each cluster. These calculated data are compared to the experimentally measured Raman spectra of ZnO 4 to identify the clusters which exist in this material. The density-functional theory in the local density approximation (LDA) is used with double numerical basis set. From this calculation, we find that the bond length for the cluster of ZnO 4 with tetrahedral symmetry (T d) is 1.923 Å and the vibrational frequencies are 94.4 cm-1 and 440.4 cm-1 with degeneracy of 3 each. We have made several clusters using zinc and oxygen atoms and have calculated the vibrational frequencies, degeneracies and intensities in each case.

Research paper thumbnail of Electronic structure and phase stability of low-temperature Ba(Fe1-xNix)2As2 superconductor

Research paper thumbnail of Vibrational frequencies of clusters: arsenic oxide, carbon nitride, copper oxide, selenium and related compounds with different atoms / Ahmad Nazrul bin Rosli

Research paper thumbnail of Clusters of GaAs prepared by quantum mechanical DFT and the nanowire raman spectra

Research paper thumbnail of DFT calculation of vibrations in the clusters of zinc and oxygen atoms

Research paper thumbnail of The Study of Band Structure of Graphite Intercalation Compound Containing Sodium Calculated Using Density Functional Theory

Journal of Physics: Conference Series, 2015

Research paper thumbnail of Density Functional Theory (DFT) Calculation of Band Structure of Kesterite

Advanced Materials Research, 2015

The kesterite, Cu2ZnSnS4 has a big potential as a future solar material in replacing current mate... more The kesterite, Cu2ZnSnS4 has a big potential as a future solar material in replacing current material. Although the kesterite and copper indium gallium selenide, CIGS has almost same structure but the constituent elements of kesterite are earth-abundance, cheaper and non-toxic. The chalcogen elements existed inside the kesterite compound are selenium and sulphur, Cu2ZnSnSe4 / Cu2ZnSnS4. Therefore, the structural flexibility of kesterite opens up an avenue to develop light-absorber material with suitable properties and applications. The density functional theory (DFT) has been used to calculate the total energy of Kesterite developed from Material Studio - CASTEP. The general gradient approximation (GGA) has been choosing to treat the exchange-correlation. The structure of kesterite has been developed by determining its space group, I4 and Pc and its coordination of each atom. The previous calculated shown that the energy of its band gap is around 1.0-1.5 eV.

Research paper thumbnail of The Raman Spectra of Nanocomposite Clusters of Atoms in Phosphorous-Selenium Glassy State

Advanced Materials Research, 2013

ABSTRACT We make clusters of atoms of the size of less than 1 nanometer by using the density func... more ABSTRACT We make clusters of atoms of the size of less than 1 nanometer by using the density functional theory and from that we obtain the bond lengths corresponding to the minimum energy configuration. We are able to optimize large clusters of atoms and find the vibrational frequencies for each cluster. This calculation provides us with a method to identify the clusters present in an unknown sample of a glass by comparing the experimental Raman frequency with the calculated value. We start with the experimental values of the Raman frequencies of PSe (Phosphorous-Selenium) glass. We calculate the structural parameters of PSe, P4Se, P2Se2, P4Se5, PSe4, P4Se3 clusters of atoms and tabulate the vibrational frequencies. We compare the calculated values with those measured. In this way we find the clusters of atoms present in the glass. Some times, the same number of atoms can be rearranged in a different symmetry. Hence we learn the symmetries of molecules. We find that certain symmetries are broken due to self-organization in the glassy state.

Research paper thumbnail of Graphene Infrared Spectroscopy: DFT Vibrational Frequencies

The band structure asymmetry in terms of positive energy solution not being equal to the negative... more The band structure asymmetry in terms of positive energy solution not being equal to the negative energy solution for the electron was found by us. The experimental work shows the gap resonance and the linear Stark effect upon application of the electric field. We have calculated the vibrational frequencies by using the density functional theory LDA for various models of graphene. The bond length in a single hexagonal carbon ring is 1.376 A˚´ and its vibrational frequency is 1062.27 cm-1. In a monolayer of 32 atoms, there are a large number of vibrations starting from 42.24 cm-1 to about 1551.32 cm-1. In another type of graphene model of 30 atoms, the frequencies calculated vary from 23.12 cm-1 to 1546.26 cm-1. In the case of the two layers of 30 atoms each, the vibrational frequencies vary from 32.55 cm-1 to 1548.23 cm-1.

Research paper thumbnail of The energy band structure of AxFe2Se2 (A = K, Rb) superconductors

ABSTRACT We study the band structure of antiferromagnetic AxFe2Se2 (A = K, Rb) superconductors by... more ABSTRACT We study the band structure of antiferromagnetic AxFe2Se2 (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of AxFe2Se2 will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the AxFe2Se2 is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level.

Research paper thumbnail of Ab initio calculation of vibrational frequencies of GexSe1−x glass

Journal of Non-Crystalline Solids, 2008

We have used the density functional theory to make the models of Ge x Se 1−x glass for which the ... more We have used the density functional theory to make the models of Ge x Se 1−x glass for which the energy is a minimum. The clusters, Ge 2 Se 2 , Ge 2 Se 3 , Ge 3 Se, Ge 3 Se 2 , Ge 4 Se, GeSe 3 , GeSe 4 , chain mode zig-zag Ge 4 Se 3 , corner sharing GeSe 4 , and edge ...

Research paper thumbnail of DFT Determination of Law of Force in Fe and P Clusters of Atoms

We use the density functional theory to make clusters of atoms of Fe with a few atoms of P and op... more We use the density functional theory to make clusters of atoms of Fe with a few atoms of P and optimize the geometry in each case. We vary the number of P atoms and determine the vibrational spectra for each cluster of atoms. We calculate the largest vibrational frequency as a function of number of P atoms. From this study we find that the force, f = -kx is not linear but shows oscillations. The oscillations arise due to the quantum mechanical orbitals which are solutions of the Schroedinger equation. We are able to determine the law of force between Fe and P atoms for several clusters of atoms.

Research paper thumbnail of DFT CALCULATION OF VIBRATIONAL FREQUENCIES IN CLUSTERS OF Fe AND As ATOMS

The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimi... more The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimize the bond lengths and angles to determine the stable structure for integer values of n and m. We calculate the vibrational frequencies for all of the clusters and hence determine the largest frequency of each cluster as a function of number of As atoms. For

Research paper thumbnail of DFT Ab initio Calculation of Vibrational Frequencies in AsSe glass

By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm)... more By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm), frequencies(intensities)[degeneracy] for various clusters of arsenic selenide. Our results are as follows. (i) AsSe(diatomic) bond length 216pm, 244.0(1/cm). (ii) As2Se(linear) bond length 228.5 pm, frequencies 27.6(1.9) and 387.6(4.3). (iii) As2Se(triangular) As-Se 243.4 pm, As-As 223.3 pm, frequencies 237.3(2.4) and 332.4(0.05)(1/cm). (iv) As3Se (triangular) bond length 238.4 pm, frequencies 107.5 and 296(weak)(1/cm). (v) As4Se (square) bond length 250.2 pm, 58.5(0.04), 241.3(5.9)(1/cm). (vi) AsSe3 (triangular), bond length 231.2 pm, 75.9(0.003), 103.5(1.26)[2], 350.9(33.2)[2]. From this study we identify that linear As-Se-As for which the calculated frequency is 27.6(1/cm) is in agreement with the data of Nemanich, Phys. Rev. B 16, 1655(1977), J. C. Phillips et al Phys. Rev B 21, 5724(1980). We have successfully calculated several vibrational frequencies accurately which agree with the Raman data. *V. R. Devi et al J. Non-Cryst. Solids 351, 489(2005);353,111(2007)

Research paper thumbnail of Von Klitzing's Constant as a Special Case of Generalized Constants

The Hall resistivity is found to become a function of spin. For positive spin, one value is found... more The Hall resistivity is found to become a function of spin. For positive spin, one value is found but for negative sign in the spin, another value occurs. In this way, there is never only one value of the resistivity but there is doubling of values. The value of the von Klitzing's constant is a special case of more general dependence of resistivity on the spin. We investigate the effect of Landau levels. For extreme quantum limit, n = 0, the effective charge of the electron becomes (1/2)ge. The fractional charge arises for finite value of the angular momentum. There is a formation of spin clusters. As the field increases, there is a phase transition from spin ½ to spin 3/2 so that g value becomes 4 and various values of n in Landau levels, g(n+1/2), form plateaus in the Hall resistivity. For finite values of the orbital angular momenta, many fractional charges emerge. The fractional as well as the integral values of the charge are in full agreement with the experimental data. The generalized constant is h/[(1/2)ge]e which under special conditions becomes h/e2 which is the von Klitzing's constant.

Research paper thumbnail of Von Klitzing’s Constant as a Special Case of Generalized Constants

The Hall resistivity is found to become a function of spin. For positive spin, one value is found... more The Hall resistivity is found to become a function of spin. For positive spin, one value is found but for negative sign in the spin, another value occurs. In this way, there is never only one value of the resistivity but there is doubling of values. The value of the von Klitzing's constant is a special case of more general

Research paper thumbnail of Density-Functional Theory of Vibrations in Ni 1− x V x Clusters

Journal of Cluster Science

We have performed the calculation of the vibrational frequencies, Fermi energy and binding energy... more We have performed the calculation of the vibrational frequencies, Fermi energy and binding energy for several clusters of Ni and vanadium atoms by using the first principles. The calculations are performed by using the density-functional theory in the local-density approximation with spin polarized orbitals. The calculation of vibrational frequencies shows that some of the clusters have positive vibrational frequencies which describe the oscillations of the stable clusters. The negative vibrational frequencies indicate that these clusters are instable with respect to these vibrations when no energy of this frequency is supplied. We find that for vanadium concentration less than 11.1% the clusters of Ni and V atoms are not stable. Hence ferromagnetism in Ni is predicted below 11.1% vanadium. We find the vibrational frequencies of several clusters for which the vanadium concentration is more than 11.1%. We are able to find a phase transition by use of quantum mechanics alone without the use of classical mechanical variables or thermodynamic variables such as temperature.

Research paper thumbnail of Ab initio calculation of vibrational frequencies and Raman spectra of barium peroxide glass including comparison of tetrahedral BaO4 with GeO4 and SiO4

Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011

We have calculated the vibrational frequencies of clusters of atoms from the first principles by ... more We have calculated the vibrational frequencies of clusters of atoms from the first principles by using the density-functional theory in the local density approximation (LDA). We are also able to calculate the electronic binding energy for all of the clusters of atoms from the optimized structure. We have made clusters of Ba nO m ( n, m = 1-6) and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO 2 occurs with the O-O vibrational frequency of 836.3 cm -1. We also find that a glass network occurs in the material which explains the vibrational frequency of 67 cm -1. The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass. We have calculated the vibrational frequencies of BaO 4, GeO 4 and SiO 4 each in tetrahedral configuration and find that the vibrational frequencies in these systems depend on the inverse square root of the atomic mass.

Research paper thumbnail of DFT Calculation of Clusters of Ba and O atoms and the Raman spectra of Barium Peroxide

We calculate the vibrational frequencies of clusters of atoms from the first principles by using ... more We calculate the vibrational frequencies of clusters of atoms from the first principles by using the density functional theory in the local-density approximation. We are also able to calculate the electronic binding energy. We have made clusters of BanOm(n = 1-5,m = 1-4) atoms and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO2 occurs with the O-O vibrational frequency at 836.3 cm-1. We also find that a glass net work occurs in the material which explains the vibration at 67 cm-1. The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass.

Research paper thumbnail of Ab Initio Calculation Of Vibrational Frequencies In AsxS1-x Glass And The Raman Spectra

We have made many different models for the understanding of the structure of AsS glass. In partic... more We have made many different models for the understanding of the structure of AsS glass. In particular, we made the models of AsS3 (triangular), AsS3 (pyramid), AsS4 (3S on one side, one on the other side of As, S3-As-S), AsS4 (pyramid), AsS4 (tetrahedral), AsS7, As2S6 (dumb bell), As2S3 (bipyramid), As2S3 (zig-zag), As3S2 (bipyramid), As3S2 (linear), As4S4 (cubic), As4S4 (ring), As4S (tetrahedral), As4S (pyramid), As4S3 (linear) and As6S2 (dumb bell) by using the density functional theory which solves the Schrödinger equation for the given number of atoms in a cluster in the local density approximation. The models are optimized for the minimum energy which determines the structures, bond lengths and angles. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the experimentally observed Raman frequencies with those calculated so that we can identify whether the cluster is present in the glass. In this way we find that AsS4 (S3-As-S), As4S4 (ring), As2S3 (bipyramid), As4S4 (cubic), As4S3 (linear), As2S3 (zig-zag), AsS4 (Td), As2S6 (dumb bell), AsS3 (triangle) and AsS3 (pyramid) structures are present in the actual glass.

Research paper thumbnail of DFT Calculation of Vibrations in the Clusters of Zinc and Oxygen Atoms (Pengiraan Getaran bagi Kluster Atom Zink dan Oksigen dengan DFT

The nanometer size clusters are often present in ZnO. We have calculated the vibrational frequenc... more The nanometer size clusters are often present in ZnO. We have calculated the vibrational frequencies of zinc oxide by using the density-functional theory. We synthesized clusters of ZnO starting with ZnO n and continue with Zn 2 O n , Zn 3 O n and Zn 4 O n with n = 1, 2, 3 and 4. By minimizing the energy of the Schrödinger equation, we found the bond lengths and the vibrational frequencies of each cluster. These calculated data are compared to the experimentally measured Raman spectra of ZnO 4 to identify the clusters which exist in this material. The density-functional theory in the local density approximation (LDA) is used with double numerical basis set. From this calculation, we find that the bond length for the cluster of ZnO 4 with tetrahedral symmetry (T d) is 1.923 Å and the vibrational frequencies are 94.4 cm-1 and 440.4 cm-1 with degeneracy of 3 each. We have made several clusters using zinc and oxygen atoms and have calculated the vibrational frequencies, degeneracies and intensities in each case.

Research paper thumbnail of Electronic structure and phase stability of low-temperature Ba(Fe1-xNix)2As2 superconductor

Research paper thumbnail of Vibrational frequencies of clusters: arsenic oxide, carbon nitride, copper oxide, selenium and related compounds with different atoms / Ahmad Nazrul bin Rosli

Research paper thumbnail of Clusters of GaAs prepared by quantum mechanical DFT and the nanowire raman spectra

Research paper thumbnail of DFT calculation of vibrations in the clusters of zinc and oxygen atoms

Research paper thumbnail of The Study of Band Structure of Graphite Intercalation Compound Containing Sodium Calculated Using Density Functional Theory

Journal of Physics: Conference Series, 2015

Research paper thumbnail of Density Functional Theory (DFT) Calculation of Band Structure of Kesterite

Advanced Materials Research, 2015

The kesterite, Cu2ZnSnS4 has a big potential as a future solar material in replacing current mate... more The kesterite, Cu2ZnSnS4 has a big potential as a future solar material in replacing current material. Although the kesterite and copper indium gallium selenide, CIGS has almost same structure but the constituent elements of kesterite are earth-abundance, cheaper and non-toxic. The chalcogen elements existed inside the kesterite compound are selenium and sulphur, Cu2ZnSnSe4 / Cu2ZnSnS4. Therefore, the structural flexibility of kesterite opens up an avenue to develop light-absorber material with suitable properties and applications. The density functional theory (DFT) has been used to calculate the total energy of Kesterite developed from Material Studio - CASTEP. The general gradient approximation (GGA) has been choosing to treat the exchange-correlation. The structure of kesterite has been developed by determining its space group, I4 and Pc and its coordination of each atom. The previous calculated shown that the energy of its band gap is around 1.0-1.5 eV.

Research paper thumbnail of The Raman Spectra of Nanocomposite Clusters of Atoms in Phosphorous-Selenium Glassy State

Advanced Materials Research, 2013

ABSTRACT We make clusters of atoms of the size of less than 1 nanometer by using the density func... more ABSTRACT We make clusters of atoms of the size of less than 1 nanometer by using the density functional theory and from that we obtain the bond lengths corresponding to the minimum energy configuration. We are able to optimize large clusters of atoms and find the vibrational frequencies for each cluster. This calculation provides us with a method to identify the clusters present in an unknown sample of a glass by comparing the experimental Raman frequency with the calculated value. We start with the experimental values of the Raman frequencies of PSe (Phosphorous-Selenium) glass. We calculate the structural parameters of PSe, P4Se, P2Se2, P4Se5, PSe4, P4Se3 clusters of atoms and tabulate the vibrational frequencies. We compare the calculated values with those measured. In this way we find the clusters of atoms present in the glass. Some times, the same number of atoms can be rearranged in a different symmetry. Hence we learn the symmetries of molecules. We find that certain symmetries are broken due to self-organization in the glassy state.

Research paper thumbnail of Graphene Infrared Spectroscopy: DFT Vibrational Frequencies

The band structure asymmetry in terms of positive energy solution not being equal to the negative... more The band structure asymmetry in terms of positive energy solution not being equal to the negative energy solution for the electron was found by us. The experimental work shows the gap resonance and the linear Stark effect upon application of the electric field. We have calculated the vibrational frequencies by using the density functional theory LDA for various models of graphene. The bond length in a single hexagonal carbon ring is 1.376 A˚´ and its vibrational frequency is 1062.27 cm-1. In a monolayer of 32 atoms, there are a large number of vibrations starting from 42.24 cm-1 to about 1551.32 cm-1. In another type of graphene model of 30 atoms, the frequencies calculated vary from 23.12 cm-1 to 1546.26 cm-1. In the case of the two layers of 30 atoms each, the vibrational frequencies vary from 32.55 cm-1 to 1548.23 cm-1.

Research paper thumbnail of The energy band structure of AxFe2Se2 (A = K, Rb) superconductors

ABSTRACT We study the band structure of antiferromagnetic AxFe2Se2 (A = K, Rb) superconductors by... more ABSTRACT We study the band structure of antiferromagnetic AxFe2Se2 (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of AxFe2Se2 will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the AxFe2Se2 is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level.

Research paper thumbnail of Ab initio calculation of vibrational frequencies of GexSe1−x glass

Journal of Non-Crystalline Solids, 2008

We have used the density functional theory to make the models of Ge x Se 1−x glass for which the ... more We have used the density functional theory to make the models of Ge x Se 1−x glass for which the energy is a minimum. The clusters, Ge 2 Se 2 , Ge 2 Se 3 , Ge 3 Se, Ge 3 Se 2 , Ge 4 Se, GeSe 3 , GeSe 4 , chain mode zig-zag Ge 4 Se 3 , corner sharing GeSe 4 , and edge ...

Research paper thumbnail of DFT Determination of Law of Force in Fe and P Clusters of Atoms

We use the density functional theory to make clusters of atoms of Fe with a few atoms of P and op... more We use the density functional theory to make clusters of atoms of Fe with a few atoms of P and optimize the geometry in each case. We vary the number of P atoms and determine the vibrational spectra for each cluster of atoms. We calculate the largest vibrational frequency as a function of number of P atoms. From this study we find that the force, f = -kx is not linear but shows oscillations. The oscillations arise due to the quantum mechanical orbitals which are solutions of the Schroedinger equation. We are able to determine the law of force between Fe and P atoms for several clusters of atoms.

Research paper thumbnail of DFT CALCULATION OF VIBRATIONAL FREQUENCIES IN CLUSTERS OF Fe AND As ATOMS

The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimi... more The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimize the bond lengths and angles to determine the stable structure for integer values of n and m. We calculate the vibrational frequencies for all of the clusters and hence determine the largest frequency of each cluster as a function of number of As atoms. For

Research paper thumbnail of DFT Ab initio Calculation of Vibrational Frequencies in AsSe glass

By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm)... more By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm), frequencies(intensities)[degeneracy] for various clusters of arsenic selenide. Our results are as follows. (i) AsSe(diatomic) bond length 216pm, 244.0(1/cm). (ii) As2Se(linear) bond length 228.5 pm, frequencies 27.6(1.9) and 387.6(4.3). (iii) As2Se(triangular) As-Se 243.4 pm, As-As 223.3 pm, frequencies 237.3(2.4) and 332.4(0.05)(1/cm). (iv) As3Se (triangular) bond length 238.4 pm, frequencies 107.5 and 296(weak)(1/cm). (v) As4Se (square) bond length 250.2 pm, 58.5(0.04), 241.3(5.9)(1/cm). (vi) AsSe3 (triangular), bond length 231.2 pm, 75.9(0.003), 103.5(1.26)[2], 350.9(33.2)[2]. From this study we identify that linear As-Se-As for which the calculated frequency is 27.6(1/cm) is in agreement with the data of Nemanich, Phys. Rev. B 16, 1655(1977), J. C. Phillips et al Phys. Rev B 21, 5724(1980). We have successfully calculated several vibrational frequencies accurately which agree with the Raman data. *V. R. Devi et al J. Non-Cryst. Solids 351, 489(2005);353,111(2007)

Research paper thumbnail of Von Klitzing's Constant as a Special Case of Generalized Constants

The Hall resistivity is found to become a function of spin. For positive spin, one value is found... more The Hall resistivity is found to become a function of spin. For positive spin, one value is found but for negative sign in the spin, another value occurs. In this way, there is never only one value of the resistivity but there is doubling of values. The value of the von Klitzing's constant is a special case of more general dependence of resistivity on the spin. We investigate the effect of Landau levels. For extreme quantum limit, n = 0, the effective charge of the electron becomes (1/2)ge. The fractional charge arises for finite value of the angular momentum. There is a formation of spin clusters. As the field increases, there is a phase transition from spin ½ to spin 3/2 so that g value becomes 4 and various values of n in Landau levels, g(n+1/2), form plateaus in the Hall resistivity. For finite values of the orbital angular momenta, many fractional charges emerge. The fractional as well as the integral values of the charge are in full agreement with the experimental data. The generalized constant is h/[(1/2)ge]e which under special conditions becomes h/e2 which is the von Klitzing's constant.

Research paper thumbnail of Von Klitzing’s Constant as a Special Case of Generalized Constants

The Hall resistivity is found to become a function of spin. For positive spin, one value is found... more The Hall resistivity is found to become a function of spin. For positive spin, one value is found but for negative sign in the spin, another value occurs. In this way, there is never only one value of the resistivity but there is doubling of values. The value of the von Klitzing's constant is a special case of more general

Research paper thumbnail of Density-Functional Theory of Vibrations in Ni 1− x V x Clusters

Journal of Cluster Science

We have performed the calculation of the vibrational frequencies, Fermi energy and binding energy... more We have performed the calculation of the vibrational frequencies, Fermi energy and binding energy for several clusters of Ni and vanadium atoms by using the first principles. The calculations are performed by using the density-functional theory in the local-density approximation with spin polarized orbitals. The calculation of vibrational frequencies shows that some of the clusters have positive vibrational frequencies which describe the oscillations of the stable clusters. The negative vibrational frequencies indicate that these clusters are instable with respect to these vibrations when no energy of this frequency is supplied. We find that for vanadium concentration less than 11.1% the clusters of Ni and V atoms are not stable. Hence ferromagnetism in Ni is predicted below 11.1% vanadium. We find the vibrational frequencies of several clusters for which the vanadium concentration is more than 11.1%. We are able to find a phase transition by use of quantum mechanics alone without the use of classical mechanical variables or thermodynamic variables such as temperature.

Research paper thumbnail of Ab initio calculation of vibrational frequencies and Raman spectra of barium peroxide glass including comparison of tetrahedral BaO4 with GeO4 and SiO4

Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011

We have calculated the vibrational frequencies of clusters of atoms from the first principles by ... more We have calculated the vibrational frequencies of clusters of atoms from the first principles by using the density-functional theory in the local density approximation (LDA). We are also able to calculate the electronic binding energy for all of the clusters of atoms from the optimized structure. We have made clusters of Ba nO m ( n, m = 1-6) and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO 2 occurs with the O-O vibrational frequency of 836.3 cm -1. We also find that a glass network occurs in the material which explains the vibrational frequency of 67 cm -1. The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass. We have calculated the vibrational frequencies of BaO 4, GeO 4 and SiO 4 each in tetrahedral configuration and find that the vibrational frequencies in these systems depend on the inverse square root of the atomic mass.

Research paper thumbnail of DFT Calculation of Clusters of Ba and O atoms and the Raman spectra of Barium Peroxide

We calculate the vibrational frequencies of clusters of atoms from the first principles by using ... more We calculate the vibrational frequencies of clusters of atoms from the first principles by using the density functional theory in the local-density approximation. We are also able to calculate the electronic binding energy. We have made clusters of BanOm(n = 1-5,m = 1-4) atoms and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO2 occurs with the O-O vibrational frequency at 836.3 cm-1. We also find that a glass net work occurs in the material which explains the vibration at 67 cm-1. The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass.

Research paper thumbnail of Ab Initio Calculation Of Vibrational Frequencies In AsxS1-x Glass And The Raman Spectra

We have made many different models for the understanding of the structure of AsS glass. In partic... more We have made many different models for the understanding of the structure of AsS glass. In particular, we made the models of AsS3 (triangular), AsS3 (pyramid), AsS4 (3S on one side, one on the other side of As, S3-As-S), AsS4 (pyramid), AsS4 (tetrahedral), AsS7, As2S6 (dumb bell), As2S3 (bipyramid), As2S3 (zig-zag), As3S2 (bipyramid), As3S2 (linear), As4S4 (cubic), As4S4 (ring), As4S (tetrahedral), As4S (pyramid), As4S3 (linear) and As6S2 (dumb bell) by using the density functional theory which solves the Schrödinger equation for the given number of atoms in a cluster in the local density approximation. The models are optimized for the minimum energy which determines the structures, bond lengths and angles. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the experimentally observed Raman frequencies with those calculated so that we can identify whether the cluster is present in the glass. In this way we find that AsS4 (S3-As-S), As4S4 (ring), As2S3 (bipyramid), As4S4 (cubic), As4S3 (linear), As2S3 (zig-zag), AsS4 (Td), As2S6 (dumb bell), AsS3 (triangle) and AsS3 (pyramid) structures are present in the actual glass.