Ahmad Nazrul Rosli

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 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...

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

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 BanOm (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 BaO2 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 BaO4, GeO4 and SiO4 each in tetrahedral configuration and find that the vibrational frequencies in these systems depend on the inverse square root of the atomic mass.

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 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 Schrodinger 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 ...

Vibrational Frequencies in AsxSe1−x Glass

The density functional theory is used to make models of clusters of atoms of arsenic and selenium. We are able to determine the bond lengths and angles for which the energy of the Schroedinger equation is minimum. The vibrational spectra of the optimized clusters are computed by using several different wave functions. It is found that the double zeta wave functions work the best. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the calculated values with those measured experimentally from the Raman spectra of As‐Se glass. The calculations have been done for many clusters, for example, (i) AsSe (diatomic), (ii) As2Se (linear), (iii) As2Se (triangular), (iv) As3Se (triangular), (v) As4Se (square), (vi) AsSe3 (triangular), etc. From this study we identify that linear As–Se–As for which the calculated frequency is 27.6 cm−1 is in agreement with the experimental data.The density functional theory is used to make models of clusters of atoms of arsenic and selenium. We are able to determine the bond lengths and angles for which the energy of the Schroedinger equation is minimum. The vibrational spectra of the optimized clusters are computed by using several different wave functions. It is found that the double zeta wave functions work the best. For the optimized clusters, we calculated the vibrational frequencies in each case by calculating the gradients of the first principles potential. We compare the calculated values with those measured experimentally from the Raman spectra of As‐Se glass. The calculations have been done for many clusters, for example, (i) AsSe (diatomic), (ii) As2Se (linear), (iii) As2Se (triangular), (iv) As3Se (triangular), (v) As4Se (square), (vi) AsSe3 (triangular), etc. From this study we identify that linear As–Se–As for which the calculated frequency is 27.6 cm−1 is in agreement with the experimental data.

Clusters of Ge and O Atoms and the Raman Spectra of Vitreous GeO2

We have constructed the clusters of atoms of germanium and oxygen atoms by using the density‐functional theory. By optimizing the structures for the minimum energy of the Kohn‐Sham equation, we are able to calculate the bond lengths. We use the local density approximation to obtain the electronic binding energy for each cluster. We find the vibrational frequencies of each and every cluster and compare the calculated values with those measured from the Raman spectra of GeO2 glass. The glass involves clustering of atoms. Hence some of the calculated values match with those found in the experimental data. In this way, we find that Ge‐O2 (triangular), Ge‐O3 (pyramidal) and Ge‐O6 (pyramidal) clusters are present in the glassy state.

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 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.

A first principle study of band structure of tetragonal barium titanate

Barium titanate (BaTiO3) is a perovskite crystal structure and it is well known to have many potential applications in microelectronic industry due to its high capabilities to enhance the performance of the capacitors and other energy storage devices. BaTiO3 has been reported to have a wide band gap around 3.4 eV from previous experimental studies. In theoretical studies, the analysis of the band structure of perovskite type of materials still under investigation due to high disagreement with the experimental result. The objective of this research is to investigate the band gap of the tetragonal BaTiO3 calculated using generalized gradient approximation (GGA) and hybrid functional (HSE03) with various pseudopotential methods performed by CASTEP module. The calculation using GGA show underestimation of energy band gap. However, the band gap calculated using HSE03 approximation shows an agreement with the experimental result.

Ab initio calculation of vibrational frequencies of ZnSe and the Raman spectra

The single layer of ZnSe has been studied to understand the structure using density functional theory. The vibrational frequencies of several cluster of ZnSe have been calculated when the Kohn-Sham equation solved at the ground state energy. We have done the calculation for 34 models of ZnSe clusters but only the stable molecules will be discussed. The bond length, Fermi energy and binding energy of ZnSe clusters have been calculated. The experimental result of single layer of ZnSe shown by Nesheva et. al. using different thickness of layers until 1μm [1]. The Raman spectra of ZnSe shown several peak for different thickness. In this paper, we will show the comparison of our calculated result with the experimental Raman spectra to show the existent of cluster.

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

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.