Density functional study of carbon vacancies in titanium carbide.

It is well established that TiC contains carbon vacancies not only in carbon-deficient environments but also in carbon-rich environments. We have performed density functional calculations of the vacancy formation energy in TiC for C- as well as Ti-rich conditions using several different approximations to the exchange-correlation functional, and also carefully considering the nature and thermodynamics of the carbon reference state, as well as the effect of varying growth conditions. We find that the formation of carbon vacancies is clearly favorable under Ti-rich conditions, whereas it is slightly energetically unfavorable under C-rich conditions.

Temperature dependence of band gaps and conformational disorder in PEDOT and its selenium and tellurium derivatives: Density functional calculations.

The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexible electronics. We present combined molecular dynamics and quantum chemical calculations, based on density functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS and EDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems. With finite size scaling, we also extrapolate our results to the infinite polymers, i.

Resistive graphene humidity sensors with rapid and direct electrical readout.

We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure.

Conformations, structural transitions and visible near-infrared absorption spectra of four-, five- and six-coordinated Cu(II) aqua complexes.

We have performed Car-Parrinello molecular dynamics simulations at ambient conditions for four-, five- and six-coordinated Cu(II) aqua complexes. The molecular geometry has been investigated in terms of Cu-O, Cu-H bond lengths and O-Cu-O bond angles and compared with earlier experimental measurement results and theoretical calculations. We find that the average Cu-O and Cu-H bond lengths increase with increasing coordination number.

Solvent dependence of conformational distribution, molecular geometry, and electronic structure in adenosine.

Solvation dynamics of adenosine in water and chloroform solvents under ambient conditions has been investigated using both force-field molecular dynamics (MD) and first-principles Car-Parrinello molecular dynamics (CPMD) calculations. First, the solvent dependence of the equilibria between anti-syn forms, C((3'))-endo-C((2'))-endo conformations, and carbinol group rotamers has been discussed from MD calculations. We find that in both the solvents the adenosine molecule can remain either in anti or syn conformations.