Correlated ab-initio calculations for ground-state properties of II-VI semiconductors

Correlated ab-initio ground-state calculations, using relativistic energy-consistent pseudopotentials, are performed for six II-VI semiconductors. Valence ($ns,np$) correlations are evaluated using the coupled cluster approach with single and double excitations. An incremental scheme is applied based on correlation contributions of localized bond orbitals and of pairs and triples of such bonds. In view of the high polarity of the bonds in II-VI compounds, we examine both, ionic and covalent embedding schemes for the calculation of individual bond increments. Also, a partitioning of the correlation energy according to local ionic increments is tested. Core-valence ($nsp,(n-1)d$) correlation effects are taken into account via a core-polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data we recover about 94% of the experimental cohesive energies; lattice constants are accurate to \sim 1%; bulk moduli are on average 10% too large compared with experiment.Comment: 10 pages, twocolumn, RevTex, 3 figures, accepted Phys. Rev.

Penggunaan Gel Lidah Buaya (Aloe Vera) sebagai Koagulan Alami dalam Penjernihan Air Sumur di Desa Sausu Tambu Kecamatan Sausu

Research on the use of aloe vera gel (aloe vera) as a natural coagulant in water purification village wells Sausu Tambu has been done. This study aims to determine whether aloe vera gel can be used as a natural coagulant and determine the optimum ratio of aloe vera gel in water (V/V) which is used in the purification of water wells in the village Sausu Tambu. Research was conducted on the water sample preparation, natural production of aloe vera gel, water treatment and analysis of water quality parameters, namely turbidity, hardness, color, pH and temperature. The results showed that aloe vera gel can be used as a coagulant to purify the water with an optimum ratio of 0.3 mL aloe vera gel in 500 mL water sample. Aloe vera gel can reduce 72.22% of turbidity, 63.48% hardness, 68.62% color with a pH of 5.5 and a temperature of 30 oC. It can be concluded that the aloe vera gel has the ability as a coagulant to purify water

Influence of electron correlations on ground-state properties of III-V semiconductors

Lattice constants and bulk moduli of eleven cubic III-V semiconductors are calculated using an ab initio scheme. Correlation contributions of the valence electrons, in particular, are determined using increments for localized bonds and for pairs and triples of such bonds; individual increments, in turn, are evaluated using the coupled cluster approach with single and double excitations. Core-valence correlation is taken into account by means of a core polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data, we obtain lattice constants which agree with experiment within an average error of -0.2%; bulk moduli are accurate to +4%. We discuss in detail the influence of the various correlation contributions on lattice constants and bulk moduli.Comment: 4 pages, Latex, no figures, Phys. Rev. B, accepte

Antibacterial Activity Potential of Kombucha Made with Faloak (Sterculia quadrifida R.Br.) Stem Bark from Timor Island

Exploration of the potential of alternative ingredients to replace black tea or green tea in making kombucha has begun to be widely carried out. On Timor Island, faloak stem bark is processed into a traditional drink by some locals. For this reason, the use of faloak stem bark as a basic ingredient for kombucha needs to be studied, especially in exploring its antibacterial potential, which is analyzed based on the concentration of sugar used. This study aims to determine the chemical characteristics and antibacterial activity of faloak stem bark kombucha with various concentrations of sugar. The methods involved making faloak stem bark kombucha with varying sugar concentrations of 6, 8, 10, and 12% (w/v), and testing chemical characteristics in the form of pH, total acid, total sugar, and total phenol tests. Meanwhile, the antibacterial activity testing used a good diffusion method against Escherichia coli ATCC 25922 bacteria. After 14 days of fermentation, faloak stem bark kombucha with a 12% sugar concentration showed the best chemical characteristics, with pH, total acid, total sugar, and total phenol values of 2.91, 1.19%, 7.33%, and 420.15 mg GAE/L, respectively. Furthermore, antibacterial activity also showed the highest inhibition (13.02 mm) at a sugar concentration of 12%. Thus, faloak bark kombucha made with a sugar concentration of 12% has the potential to be antibacterial

Cohesive energies of cubic III-V semiconductors

Cohesive energies for twelve cubic III-V semiconductors with zincblende structure have been determined using an ab-initio scheme. Correlation contributions, in particular, have been evaluated using the coupled-cluster approach with single and double excitations (CCSD). This was done by means of increments obtained for localized bond orbitals and for pairs and triples of such bonds. Combining these results with corresponding Hartree-Fock data, we recover about 92 \% of the experimental cohesive energies.Comment: 16 pages, 1 figure, late

The Gaussian formula and spherical aberration of the static and moving curved mirrors from Fermat's principle

The Gaussian formula and spherical aberrations of the static and relativistic curved mirrors are analyzed using the optical path length (OPL) and Fermat's principle. The geometrical figures generated by the rotation of conic sections about their symmetry axes are considered for the shapes of the mirrors. By comparing the results in static and relativistic cases, it is shown that the focal lengths and the spherical aberration relations of the relativistic mirrors obey the Lorentz contraction. Further analysis of the spherical aberrations for both static and relativistic cases have resulted in the information about the limits for the paraxial approximation, as well as for the minimum speed of the systems to reduce the spherical aberrations.Comment: 15 pages, 7 figures, uses iopart. Major revisions on the physical interpretations of the results. Accepted for publication in J. Op

Ground-state properties of rutile: electron-correlation effects

Electron-correlation effects on cohesive energy, lattice constant and bulk compressibility of rutile are calculated using an ab-initio scheme. A competition between the two groups of partially covalent Ti-O bonds is the reason that the correlation energy does not change linearly with deviations from the equilibrium geometry, but is dominated by quadratic terms instead. As a consequence, the Hartree-Fock lattice constants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.Comment: 1 figure to appear in Phys. Rev.