Molly De Raychaudhury

Moderate to large magneto-optical signals in high Tc double perovskites

Using first-principles density functional calculations, we have computed the optical and magneto-optical properties of the Cr-based double perovskite compounds, Sr2CrB′O6 with B′=W,Re,Os. Our computed magneto-optic spectra show substantially large Kerr rotations of about −2° to −2.5° for Sr2CrWO6 and Sr2CrReO6 and a moderately large Faraday rotation of about −0.25×106deg∕cm in insulating Sr2CrOsO6, indicating possible industrial applications. Our study should motivate experimental investigations in this yet to be explored area of Sr2CrB′O6 compounds.

Negative temperature coefficient of resistance in a crystalline compound

Resistivity measurements and temperature-dependent X-ray structural analyses are reported for the crystalline compounds GdPd3BxC1- x. We show that a controlled tuning of the temperature coefficient of resistance (TCR) can be done by modifying the structural parameters and chemical environment of the compounds. We have achieved the result of negative TCR in an ordered, non-Kondo crystalline compound. Electronic-structure calculations have been carried out to elucidate some of our observations.

Quantum Chemical Studies on Stability and Chemical Activities in Calcium Ion Bound Calmodulin Loops

Quantum chemical (QC) calculations for macromolecules require truncation of the molecule, highlighting the portion of interest due to heavy computation cost. As a result, an estimation of the effects of truncation is important to interpret the energy spectrum of such calculations. We perform density functional theory based QC calculations on calcium ion bound EF-hand loops of Calmodulin isolated from the crystal structure in an implicit solvent. We find that the terminal contributions of neutral capping are negligible across the entire ground-state energy spectrum. The coordination energy range and the nature of hybridization of the coordination state molecular orbitals remain qualitatively similar across these loops. While the HOMO and LUMO of loops in the N-terminal domain are dominated by the acidic aspartates, and the polar/hydrophobic residues, respectively, these levels of the C-terminal domain loops show strong localized electron density on the phenyl rings of the tyrosines. The Fukui index calculation identifies the hydroxyl oxygen in the phenyl ring of Y99 as a potent nucleophile. Our analysis indicates a general way of interpreting the electronic energy spectra to understand stability and functions of large biomolecules where the truncation of the molecule and, hence, the terminal capping effects are inevitable.

Origin of ferromagnetism and its pressure and doping dependence in Tl2Mn2O7.

Using the Nth order muffin-tin obital downfolding technique, we investigate the origin of ferromagnetism in pyrochlore Tl2Mn2O7. It is found to be driven by a hybridization induced spin polarization of delocalized charge carriers derived from Tl-s and O-p states. The mean-field estimate of the ferromagnetic transition temperature Tc estimated using computed exchange integrals are found to be in good agreement with measurements. We find an enhancement of Tc for moderate doping with nonmagnetic Sb and a suppression of Tc upon application of pressure, both in agreement with experimental findings.

Electronic structure and transport properties of early transition metal tripledeckers

The electronic structure and transport properties of the Cp(2)BzM(2) (M = Sc, Ti, and V) tripledeckers are studied by spin polarized density functional theory and nonequilibrium Greens function method considering high-spin and low-spin states. Total energy calculations show that the sandwich structured Cp(2)BzSc(2) exists in a singlet state with no local magnetic moment on the Sc atoms. Cp(2)BzTi(2) in triplet state exists as a distorted tripledecker and is more stable than singlet and quintet states. Cp(2)BzV(2) stabilizes in the quintet state with a spin density of 2.4 on each vanadium atom. Hunds coupling plays a vital role in stabilizing the higher multiplets in case of titanium and vanadium clusters. In bigger clusters like Cp(3)Bz(2)M(4), Sc multidecker has one unpaired spin, Ti multidecker has five unpaired spins, and V multidecker has seven unpaired spins in total. Spin polarized electronic transport is found for all states of vanadium tripledecker and one state of the titanium tripledecker when connected to a gold two probe junction. Moderate to high-spin filter efficiencies are calculated for these states. Cp(2)BzSc(2) shows spin-independent electronic transport for all electronic states when introduced in the gold two probe junction. Current versus voltage curves are reported for selected clusters in the two probe setup.

Quantum chemical studies on nucleophilic sites in calcium ion bound zwitterionic calmodulin loops

We perform quantum chemical (QC) calculations based on the density functional theory (DFT) approach for biologically relevant zwitterionic polypeptides, comprising of isolated calcium (Ca2+) ion bound EF-hand loops of calmodulin (CaM). The HOMO and the LUMO levels are observed to be dominated by terminal capping contributions which fall off exponentially in neighboring energy levels. These levels with negligible capping contributions are considered as HOMO− and LUMO+. In loop 1 and loop 2 of CaM, HOMO− and LUMO+ are dominated by acidic aspartates and polar residues whereas only polar side chains contribute in the energy levels of loop 3 and loop 4. We find that the HOMO− of loop 3 shows strong localized electron density on the side chain phenyl ring of tyrosine. This is an indication of potential nucleophilic sites for tyrosine phosphorylation in CaM. Our calculation provides a systematic way of interpreting the functionality of zwitterionic polypeptides at physiological conditions from the electronic energy spectra. Moreover, the capping levels indicate possible device applications.

Origin Of Ferromagnetism In Tl2Mn2O7 And CuCr2S4

We show that the kinetic‐energy driven exchange mechanism similar to that operative in double perovskite compound, Sr2FeMoO6, is also effective in metallic ferromagnets, Tl2Mn2O7 and CuCr2S4. The electronic structure of the two metals is analyzed in terms of N‐th order muffintin orbital method and the subtle manner in which the mechanism manifests itself in each of these compounds is discussed.

Theoretical study of dopedTl2Mn2O7andTl2Mn2O7under pressure

Using first-principles density functional based calculations, we study the effect of doping and pressure in manganese based pyrochlore compound,Tl

Theoretical study of doped Tl 2 Mn 2 O 7 and Tl 2 Mn 2 O 7 under pressure

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Theoretical study of doped-Tl

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