pH-Dependent Distribution of Functional Groups on Titanium-Based MXenes.

MXenes are a new rapidly developing class of two-dimensional materials with suitable properties for a broad range of applications. It has been shown that during synthesis of these materials the surfaces are usually functionalized by O, OH, and F and further suggested that controlling the surface allows controlling the material properties. However, a proper understanding of the surface structure is still missing, with a significant discrepancy between computational and experimental studies.

Plasmon Excitations in Mixed Metallic Nanoarrays.

Features of the surface plasmon from macroscopic materials emerge in molecular systems, but differentiating collective excitations from single-particle excitations in molecular systems remains elusive. The rich interactions between single-particle electron-hole and collective electron excitations produce phenomena related to the chemical physics aspects within the atomic array. We study the plasmonic properties of atomic arrays of noble (Au, Ag, and Cu) and transition-metal (Pd, Pt) homonuclear chains using time-dependent density functional theory and their Kohn-Sham transition contributions.

Plasmon-Induced Direct Hot-Carrier Transfer at Metal-Acceptor Interfaces.

Plasmon-induced hot-carrier transfer from a metal nanostructure to an acceptor is known to occur via two key mechanisms: (i) indirect transfer, where the hot carriers are produced in the metal nanostructure and subsequently transferred to the acceptor, and (ii) direct transfer, where the plasmons decay by directly exciting carriers from the metal to the acceptor. Unfortunately, an atomic-level understanding of the direct-transfer process, especially with regard to its quantification, remains elusive even though it is estimated to be more efficient compared to the indirect-transfer process. This is due to experimental challenges in separating direct from indirect transfer as both processes occur simultaneously at femtosecond time scales.

Alkali Postdeposition Treatment-Induced Changes of the Chemical and Electronic Structure of Cu(In,Ga)Se Thin-Film Solar Cell Absorbers: A First-Principle Perspective.

The effects of alkali postdeposition treatment (PDT) on the valence band structure of Cu(In,Ga)Se (CIGSe) thin-film solar cell absorbers are addressed from a first-principles perspective. In detail, experimentally derived hard X-ray photoelectron spectroscopy (HAXPES) data [ Handick , E. ; ACS Appl.

Kohn-Sham Decomposition in Real-Time Time-Dependent Density-Functional Theory: An Efficient Tool for Analyzing Plasmonic Excitations.

Electronic excitations can be efficiently analyzed in terms of the underlying Kohn-Sham (KS) electron-hole transitions. While such a decomposition is readily available in the linear-response time-dependent density-functional theory (TDDFT) approaches based on the Casida equations, a comparable analysis is less commonly conducted within the real-time-propagation TDDFT (RT-TDDFT). To improve this situation, we present here an implementation of a KS decomposition tool within the local-basis-set RT-TDDFT code in the free GPAW package.

Theory and Applications of Generalized Pipek-Mezey Wannier Functions.

The theory for the generation of Wannier functions within the generalized Pipek-Mezey approach (Lehtola, S.; Jónsson, H. J.

Resistive Switching in All-Oxide Ferroelectric Tunnel Junctions with Ionic Interfaces.

Universal, giant and nonvolatile resistive switching is demonstrated for oxide tunnel junctions with ferroelectric PbZr0.2 Ti0.8 O3 , ferroelectric BaTiO3, and paraelectric SrTiO3 tunnel barriers.

Degree of conversion and leached monomers of urethane dimethacrylate-hydroxypropyl methacrylate-based dental resin systems.

The degree of conversion (DC) and monomer leaching of three experimental urethane dimethacrylate (UEDMA)-hydroxypropyl methacrylate (HPMA)-based resin systems were studied. Three experimental resins (E1: 70.6 wt% UEDMA + 27.

Morphological and mechanical characterization of composite bone cement containing polymethylmethacrylate matrix functionalized with trimethoxysilyl and bioactive glass.

Medical polymers of biostable nature (e.g. polymethylmetacrylate, PMMA) are widely used in various clinical applications.

Quantized Evolution of the Plasmonic Response in a Stretched Nanorod.

Quantum aspects, such as electron tunneling between closely separated metallic nanoparticles, are crucial for understanding the plasmonic response of nanoscale systems. We explore quantum effects on the response of the conductively coupled metallic nanoparticle dimer. This is realized by stretching a nanorod, which leads to the formation of a narrowing atomic contact between the two nanorod ends.

Impact of Ga-V Codoping on Interfacial Electron Transfer in Dye-Sensitized TiO2.

The improvement of charge transfer between an organic molecule and a semiconductor is an important and challenging goal in the fields of photovoltaics and photocatalysis. In this work, we present a time-dependent density functional theory investigation of the impact of Ga-V codoping of TiO2 on the excited-state electron injection from perylene-3-carboxylic acid. The doping is shown to raise the charge-transfer efficiency for the highest possible surface dye uptake by ∼16%.

Nanoplasmonics simulations at the basis set limit through completeness-optimized, local numerical basis sets.

We present an approach for generating local numerical basis sets of improving accuracy for first-principles nanoplasmonics simulations within time-dependent density functional theory. The method is demonstrated for copper, silver, and gold nanoparticles that are of experimental interest but computationally demanding due to the semi-core d-electrons that affect their plasmonic response. The basis sets are constructed by augmenting numerical atomic orbital basis sets by truncated Gaussian-type orbitals generated by the completeness-optimization scheme, which is applied to the photoabsorption spectra of homoatomic metal atom dimers.

Enhancing conductivity of metallic carbon nanotube networks by transition metal adsorption.

The conductivity of carbon nanotube thin films is mainly determined by carbon nanotube junctions, the resistance of which can be reduced by several different methods. We investigate electronic transport through carbon nanotube junctions in a four-terminal configuration, where two metallic single-wall carbon nanotubes are linked by a group 6 transition metal atom. The transport calculations are based on the Green's function method combined with the density-functional theory.

Pick-off annihilation of positronium in matter using full correlation single particle potentials: solid He.

We investigate the modeling of positronium (Ps) states and their pick-off annihilation trapped at open volumes pockets in condensed molecular matter. Our starting point is the interacting many-body system of Ps and a He atom because it is the smallest entity that can mimic the energy gap between the highest occupied and lowest unoccupied molecular orbitals of molecules, and yet the many-body structure of the HePs system can be calculated accurately enough. The exact-diagonalization solution of the HePs system enables us to construct a pairwise full-correlation single-particle potential for the Ps-He interaction, and the total potential in solids is obtained as a superposition of the pairwise potentials.

[Biomaterials in bone repair].

In orthopedics, traumatology, and craniofacial surgery, biomaterials should meet the clinical demands of bone that include shape, size and anatomical location of the defect, as well as the physiological load-bearing stresses. Biomaterials are metals, ceramics, plastics or materials of biological origin. In the treatment of large defects, metallic endoprostheses or bone grafts are employed, whereas ceramics in the case of small defects.

Surface modification of fiber reinforced polymer composites and their attachment to bone simulating material.

The purpose of this study was to investigate the effect of fiber orientation of a fiber-reinforced composite (FRC) made of poly-methyl-methacrylate (PMMA) and E-glass to the surface fabrication process by solvent dissolution. Intention of the dissolution process was to expose the fibers and create a macroporous surface onto the FRC to enhance bone bonding of the material. The effect of dissolution and fiber direction to the bone bonding capability of the FRC material was also tested.

Nonadiabatic Ehrenfest molecular dynamics within the projector augmented-wave method.

We derive equations for nonadiabatic Ehrenfest molecular dynamics within the projector augmented-wave (PAW) formalism. The discretization of the electrons is time-dependent as the augmentation functions depend on the positions of the nuclei. We describe the implementation of the Ehrenfest molecular dynamics equations within the real-space PAW method.

Bioactive composite for keratoprosthesis skirt.

In this study, the fabrication and properties of a synthetic keratoprosthesis skirt for use in osteo-odonto-keratoprosthesis (OOKP) surgery are discussed. In the search for a new material concept, bioactive glass and polymethyl methacrylate (PMMA)-based composites were prepared. Three different bioactive glasses (i.

All-electron time-dependent density functional theory with finite elements: time-propagation approach.

We present an all-electron method for time-dependent density functional theory which employs hierarchical nonuniform finite-element bases and the time-propagation approach. The method is capable of treating linear and nonlinear response of valence and core electrons to an external field. We also introduce (i) a preconditioner for the propagation equation, (ii) a stable way to implement absorbing boundary conditions, and (iii) a new kind of absorbing boundary condition inspired by perfectly matched layers.

Electronic structure calculations with GPAW: a real-space implementation of the projector augmented-wave method.

Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.

Tunability of the optical absorption in small silver cluster-polymer hybrid systems.

We have calculated the absorption characteristics of different hybrid systems consisting of Ag, Ag(2), or Ag(3) atomic clusters and poly(methacrylic acid) using the time-dependent density-functional theory. The polymer is found to have an extensive structural-dependency on the spectral patterns of the hybrid systems relative to the bare clusters. The absorption spectrum can be "tuned" to the visible range for hybrid systems with an odd number of electrons per silver cluster, whereas for hybrid systems comprising an even number of electrons per silver cluster, the leading absorption edge can be shifted up to approximately 4.

Intrinsic n-type behavior in transparent conducting oxides: a comparative hybrid-functional study of In2O3, SnO2, and ZnO.

We present a comparative study of oxygen vacancies in In2O3, SnO2, and ZnO based on the hybrid-functional method within the density-functional theory (DFT). For In2O3 and SnO2, our results provide strong evidence of shallow donor states at oxygen vacancies. In comparison with the (semi)local exchange-correlation approximations in DFT, the hybrid-functional method strongly lowers the formation energy of the positive charge state and keeps that of the neutral state nearly intact.

All-electron density functional theory and time-dependent density functional theory with high-order finite elements.

We present for static density functional theory and time-dependent density functional theory calculations an all-electron method which employs high-order hierarchical finite-element bases. Our mesh generation scheme, in which structured atomic meshes are merged to an unstructured molecular mesh, allows a highly nonuniform discretization of the space. Thus it is possible to represent the core and valence states using the same discretization scheme, i.

Time-dependent density-functional theory in the projector augmented-wave method.

We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we found perfect agreement in the calculated photoabsorption spectra. We discuss the strengths and weaknesses of the two methods as well as their convergence properties.

Photoabsorption spectra of small fullerenes and Si-heterofullerenes.

We study the spectral properties of two kinds of derivatives of the carbon fullerene C(60), small fullerenes and Si-heterofullerenes, by ab initio calculations. The principal method of study is the time-dependent density-functional theory in its full time-propagation form. C(20), C(28), C(32), C(36), and C(50), the most stable small fullerenes in the range of C(20)-C(50), are found to have characteristic features in their optical absorption spectra, originating from the geometry of the molecules in question.