Electronic properties of alpha -quartz under pressure

Intruder Peak-Free Transient Inner-Shell Spectra Using Real-Time Simulations

Real-time methods are convenient for simulating core-level absorption spectra but suffer from nonphysical intruder peaks when using atom-centered basis sets. In transient absorption spectra, these peaks exhibit highly nonphysical time-dependent modulations in their energies and oscillator strengths. In this paper, we address the origins of these intruder peaks and propose a straightforward and effective solution based on a filtered dipole operator. In combination with real-time time-dependent density functional theory (RT-TDDFT), we demonstrate how to compute intruder-free attosecond transient X-ray absorption spectra for the aminophenol (C₆H₇NO) oxygen and nitrogen K-edges and the α-quartz (SiO₂) silicon L-edge. Without filtering, the computed spectra are qualitatively wrong. This procedure is suitable for both static and transient inner-shell spectroscopy studies and can easily be implemented in a range of real-time methodologies.

Extreme electron transport suppression in siloxane ring-based molecular devices

Siloxane ring-based molecular devices possess excessive transport suppression and size-dependent transport decay, based on an analysis of electronic coupling.

Volume dependence of the dielectric properties of amorphous SiO2

The dielectric properties of amorphous SiO₂ and other SiO₂ polymorphs are linked by simple volume dependence.

In search of new reconstructions of (001) α-quartz surface: a first principles study

Using Born–Oppenheimer molecular dynamics simulations and “static” density functional theory calculations, reconstructions of the (001) α-quartz surface are studied in detail.

Characterization of the Structural and Electronic Properties of Crystalline Lithium Silicates

Density functional theory (DFT) calculations within the generalized gradient approximation (GGA) were performed to study the atomic and electronic structure of lithium silicate crystals that were fully optimized within the theory. It is found that the relative stability of two crystalline forms of lithium disilicate agrees well with experimental results. The calculated electronic density of states shows distinguishable contributions to the oxygen 2s and upper valence bands associated with bridging (BO) and nonbridging oxygen (NBO) atoms. Bond ionicity, characterized by determining the relative atomic charges, is used to distinguish BO and NBO atoms as well as the corresponding Si-BO and Si-NBO bonds. Results from this work reveal that atomic charges obtained by using population analysis methods based on electron deformation density rather than total electron density provide an accurate description of bond ionicity consistent with chemical intuition.

Structure, dynamics, and electronic properties of lithium disilicate melt and glass

Ab initio molecular dynamics simulations within the framework of density functional theory have been performed to study the structural, dynamic, and electronic properties of lithium disilicate melt and the glass derived from quenching the melt. It is found that lithium ions have a much higher diffusion coefficient and show different diffusion mechanisms than the network forming silicon and oxygen ions in the melt. The simulated lithium disilicate glass structure has 100% four coordinated silicon, close to theoretical nonbridging oxygen to bridging oxygen ratio (2:3), and Q(n) distributions of 20.8%, 58.4%, and 20.8% for n=2,3,4, respectively. In the melt there are considerable amounts (10%-15%) of silicon coordination defects; however, the average silicon coordination number remains about 4, similar to that in the glass. The lithium ion coordination number increases from 3.7 in the glass to 4.4 in the melt mainly due to the increase of bridging oxygen in the first coordination shell. The bond length and bond angle distributions, vibrational density of states, and static structure factors of the simulated glass were determined where the latter was found to be in good agreement with experimental measurement. Atomic charges were obtained based on Bader and Hirshfeld population analyses [Atoms in Molecule: A Quantum Theory (Oxford University Press, Oxford, 1990); Theor. Chim. Acta 44, 129 (1977)]. The average Bader charges found in lithium disilicate glass were -1.729, 3.419, and 0.915 for oxygen, silicon, and lithium, respectively. The corresponding Hirshfeld charges were -0.307, 0.550, and 0.229. The electronic densities of states of the melt and glass were calculated and compared with those of crystalline lithium disilicate.