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Abu Md. Asaduzzaman

Bio: Abu Md. Asaduzzaman is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Adsorption & Cluster (physics). The author has an hindex of 19, co-authored 48 publications receiving 768 citations. Previous affiliations of Abu Md. Asaduzzaman include Penn State Harrisburg & University of Arizona.


Papers
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Journal ArticleDOI
TL;DR: It is found that the in-plane plasma frequency of the gold thin film decreases with decreasing thickness and that the optical permittivity tensor is highly anisotropic as well as thickness dependent.
Abstract: Physical properties of materials are known to be different from the bulk at the nanometer scale. In this context, the dependence of optical properties of nanometric gold thin films with respect to film thickness is studied using density functional theory (DFT). We find that the in-plane plasma frequency of the gold thin film decreases with decreasing thickness and that the optical permittivity tensor is highly anisotropic as well as thickness dependent. Quantitative knowledge of planar metal film permittivity's thickness dependence can improve the accuracy and reliability of the designs of plasmonic devices and electromagnetic metamaterials. The strong anisotropy observed may become an alternative method of realizing indefinite media.

56 citations

Journal ArticleDOI
TL;DR: For the first time, the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders is proved and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.
Abstract: In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.

52 citations

Journal ArticleDOI
TL;DR: In this paper, the structural properties of the amorphous geopolymer binder phase were examined as a function of the underlying silicon to aluminum ratio using molecular dynamics (MD) simulations.
Abstract: The amorphous geopolymer binder-phase is the primary adhesive constituent within a geopolymer and consists of completely polymerized glassy networks of (SiO 4 ) and (AlO 4 ) − tetrahedra as well as interstitial charge-balancing alkali cations. In this context, the mechanical properties of the geopolymer binder-phase were examined as a function of the underlying silicon to aluminum ratio using molecular dynamics (MD) simulations. Detailed structural analysis reveals that the presence of edge-sharing (AlO 4 ) − tetrahedra, nanoscale voids as well as non-bridging oxygen and penta coordinated aluminum atoms significantly impact the ensuing elastic moduli, ultimate tensile strength and the nature of failure of the geopolymer binder-phase. In particular, the simulations indicate that there is an optimal silicon to aluminum ratio (~ 2–3) that results in enhanced mechanical properties. This study provides, for the first time, valuable insight into the structural mechanisms that are responsible for the strength and mechanical properties of the geopolymer binder-phase.

47 citations

Journal ArticleDOI
TL;DR: Density functional theory calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury complexes with free cysteine and seleonocysteine, and the preferred degradation of the CH(3)Hg-L-cysteinate suggests that another mechanism for Hg to cross the blood-brain barrier should exist.
Abstract: Density functional theory (DFT) calculations have been carried out on the possible degradation/demethylation mechanism of methyl mercury (CH3Hg+) complexes with free cysteine and seleonocysteine. T...

41 citations

Journal ArticleDOI
TL;DR: In this paper, periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO(2) rutile (110) surface were performed, and two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered.
Abstract: To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO(2) rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta- or hexa-coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H(2)O, OH(-), and CO(3)(2-) ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface-[UO(2)(H(2)O)(3)](2+) system were well reproduced by our calculations. With respect to adsorbates, [UO(2)(L1)(x)(L2)(y)(L3)(z)](n) (L1=H(2)O, L2=OH(-), L3=CO(3)(2-), x≤3, y≤3, z≤2, x+y+2z≤4), on the ideal surface, the variation of ligands from H(2)O to OH(-) and CO(3)(2-) lengthens the U-O(surf) and U-Ti distances. As a result, the uranyl-surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO(2) decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U=O distances that are longer than those of aquouranyl species by 0.1-0.3 A. Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U=O bond lengths, shorter uranyl-surface separations in most cases, and stronger sorption interactions.

37 citations


Cited by
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
TL;DR: A large body of appropriate calculations now exists and its main conclusions are summarized in this critical review of the recent reviews by Pyykkö (2004, 2005).
Abstract: Gold is an element whose unique properties are strongly influenced by relativistic effects. A large body of appropriate calculations now exists and its main conclusions are summarized in this critical review. The present paper completes the recent reviews by Pyykko (2004, 2005) (529 references).

613 citations

Journal ArticleDOI
TL;DR: In this paper, the physics behind the two-way coupling from the electrical to the mechanical domain through the piezoelectric actuator, where an electrical signal is transformed into a mechanical deformation of the printhead structure, is discussed.

481 citations

Journal ArticleDOI
TL;DR: In this review two general types of nanoparticle-polymer PV cells are considered and compared in detail, and two sets of assembly conditions that are suggested are suggested for constructing PCBM-P3HT (P3 HT is poly(3-hexylthiophene)) or CdSe-P 3HT PV cells with reasonable power conversion efficiency.

468 citations