Computational Studies of New Materials II

The following sections are included:

• Preface

• Contents

• List of Contributors

• Introduction

The study of phenomena induced by laser radiation in both continuous (CW) and pulsed modes on solid surfaces is a widely-explored subject of modern solid-state physics and chemistry. Since the advent of the first laser in the 1960s, a huge number of scientific papers have been devoted to the investigation of different kinds of laser-matter processes, such as laser-induced damage, plasma formation, phase transitions, micro- and macroprocessing, laser-induced chemical reactions at gas–solid and liquid-solid, etc. These efforts have resulted in new laser applications in industry, e.g. cutting, welding and hardening. The laser has become a useful tool for initiating unique chemical reactions to produce advanced materials, like ultrahard ones for example. A number of technological applications, such as laser-induced deposition of metals on porous materials and semiconductor surfaces, already exist in the high-tech industry of micro- and nanoelectronics. Production of catalyzers with tailored properties of different nanostructures and components is prevalent in the chemical industry.

Many years of theoretical and experimental investigations in this area have resulted in a host of valuable physical and chemical discoveries leading to the creation of new sciences, e.g., femtochemistry. The technical development of lasers has yielded a new class of instruments — fs lasers — which are able to produce extra high (TW/cm²) intensities within the focal spot on targets. Ultrashort lasers are becoming the source of different nonlinear events with high impact on contemporary science, such as on the study of events happening in states far from equilibrium and in nonlinear circumstances. In this chapter, we discuss fs laser-matter interactions, including the production and properties of different nanostructures.

Ultrashort laser pulses create very strong laser fields which can be used as a powerful tool to manipulate material properties. Modeling material responses in nanosize dimensions and on unprecedented short time scales imposes several challenges. In this chapter, we study two models to describe the laser pulse interaction with nanomaterials in the femtosecond, picosecond and nanosecond regimes. Also, we introduce a new mechanism of ultrashort pulse/nanomaterial interactions — laser-induced explosion of absorbing nanoparticles in strong laser fields. This mechanism is realized through fast overheating of a strongly-absorbing target during the time of an ultrashort laser pulse when the influence of heat diffusion is minimal. On the basis of simple energy balance, it is found that the threshold laser energy density for thermal explosion of different gold nanoparticles is in the range 25–40 mJ/cm². Explosion of nanoparticles may be accompanied by optical plasma, generation of shock waves with supersonic expansion, and particle fragmentation with fragments of high kinetic energy.

Selectively exciting a normal mode in a large molecule by an ultrafast laser is important to many laser-engineered processes such as chemical reactions, but with so many degrees of freedom such selection is often challenging. It is shown here that the normal-mode selectivity can be achieved to some degree in C₆₀ by carefully tuning laser parameters. Two methods are identified to selectively excite infrared modes. The first is to directly excite them by resonant excitation, and the second relies on the laser pulse duration with a slightly off-resonant laser frequency. These methods can be directly tested experimentally through time-resolved absorption spectra.

In this chapter, we present a short account of some recent development of self-interaction-free density functional theory (DFT) and time dependent density functional theory (TDDFT) for accurate and efficient treatment of the electronic structure, and time-dependent quantum dynamics of many-electron atomic and molecular systems. In addition we present several advanced numerical techniques for efficient and high precision treatment of the self-interaction-free DFT/TDDFT equations. The usefulness of these procedures is illustrated by a few case studies of atomic and molecular processes in intense ultrashort laser fields, a subject of much current interest in strong-field atomic and molecular physics as well as attosecond science and technology.

Nanoparticles are being researched as a noninvasive method for selectively killing cancer cells. With particular antibody coatings on nanoparticles, they attach to the abnormal cells of interest (cancer or otherwise). Once attached, nanoparticles can be heated with UV/visible/IR or RF pulses, heating the surrounding area of the cell to the point of death. Researchers often use single-pulse or multipulse lasers when conducting nanoparticle ablation research. The laser heating of nanoparticles is very sensitive to the time structure of the incident pulsed laser radiation, the time interval between the pulses, and the number of pulses used in the experiments. In this chapter, time-dependent simulations and detailed analyses are carried out for different nonstationary pulsed laser-nanoparticle interaction modes, and the advantages and disadvantages of multipulse (set of short pulses) and single-pulse laser heating of nanoparticles are shown. A comparative analysis for both radiation modes (single-pulse and multipulse) are discussed for laser heating of metal nanotargets on nanosecond, picosecond and femtosecond time scales to make recommendations for efficient laser heating of nanomaterials in nanomedicine experiments.

The application of nanotechnology for laser thermal-based killing of abnormal cells (e.g., cancer cells) targeted with absorbing nanoparticles (e.g., gold solid nanospheres, nanoshells or nanorods) is becoming an extensive area of research. In this chapter, we develop a theory for selective laser nanophotothermolysis of abnormal biological cells with gold nanoparticles and self-assembled nanoclusters. The theory takes into account laser-induced linear and nonlinear synergistic effects in biological cells containing nanostructures, with focus on optical, thermal, bubble formation and nanoparticle explosion phenomena. On the basis of the developed models, we discuss new ideas and new dynamic modes for cancer treatment by laser activated nanoheaters, involving nanoclusters aggregation in living cells, microbubbles overlapping around laser heated intracellular nanoparticles/clusters, and laser thermal explosion mode of single nanoparticles —“nanobombs”— delivered to the cells.

Thromboembolitic diseases, such as myocardial infarction, stroke and deep vein thrombosis, are a leading cause of death throughout the world. The past two decades have seen a great deal of progress in the development of antithrombotic agents, spurred by the severity of the problem and the medical need for life-saving treatments [1]. Three treatment approaches are the development of (1) antiplatelet agents, (2) compounds that aid in the lysis of blood clots, and (3) agents that affect the activity and generation of thrombin. Thrombin is a serine protease enzyme that is responsible for many aspects in the blood coagulation cascade. Many agents have been developed to control the generation of thrombin, including heparin, low molecular weight heparins and natural and semisynthetic thrombin inhibitors such as hirudin and hirulog. These agents all have the disadvantage that they must be administered as either intravenous infusions in a hospital or as subcutaneous injections several times a day. Warfarin is an oral agent utilized as an anticoagulant because of its effects on the vitamin-K-dependent coagulation pathway. Some disadvantages of warfarin include a slow onset of action, the need for dietary restrictions, and the possibility of drug-drug interactions. The need for better agents that can be used orally with infrequent patient monitoring still exists and has stimulated a great deal of interest in the pursuit of small-molecule inhibitors of thrombin. Direct thrombin inhibitors have been developed and tested in clinical trials for a variety of these thrombotic disorders. However, the numerous biochemical reactions that take place leading to the formation and lysis of clots, and the exact influence of hemodynamic factors in these reactions, are incompletely understood [2]. Mathematical modeling provides the opportunity to integrate and quantify reaction details which, in turn, aids in the design of the more expensive empirical experiments.

In this chapter, some of the direct thrombin inhibitors (DTIs) like argatroban, hirudin and melagatran are taken under study, and their effect on the thrombin formation is investigated. Toward this aim, a recent mathematical model [3] developed on the base of the biochemical reactions of both intrinsic and extrinsic pathways of the blood coagulation system is considered, in which new reactions corresponding to DTIs are introduced.

In this chapter, time-dependent thermal simulations are performed for short and ultrashort pulse laser ablation of biological tissue in singlepulse and multipulse (set of ultrashort pulses) modes of laser heating. A comparative analysis for both radiation modes is discussed for laser heating of different types of biological tissues: cancerous and healthy cell organelles in soft tissue and solid hard tissue, such as those found in bone and teeth, on the nanosecond, picosecond and femtosecond time scales. It is shown that ultrashort laser pulses with high-energy densities can ablate the biological tissue without heating tissues bordering the ablation creator. This reaction is particularly desirable as heat accumulation and thermal damage are the main factors affecting tissue regrowth rates, and thus patient recovery times.

This article reviews our application of molecular dynamics simulation to including protein flexibility in molecular docking, particularly in studying protein kinase and phosphatase systems. It demonstrates that incorporating protein flexibility could improve the identification of correct docking pose, help study the different protein conformations induced by the binding of diverse ligands, and provide insights into molecular docking pathways in atomic detail.

An electric field-induced spin accumulation phenomenon is presented for electroluminescent conjugated polymers as light-emitting diodes (LEDs). When an electric field is applied along a polymer chain and exceeds a critical value, it quenches the luminescence and dissociates the singlet exciton into two carriers with opposite spin signs. Simultaneously, the field drives these two opposite spin carriers to move in opposite directions, leading to spin accumulation at the two ends of the organic material LED, which can be detected through Kerr rotation microscopy. Two optically-controlled spin transfer effects are proposed for π-conjugated polymers. When such a polymeric molecule undergoes two-photon excitation, the charge of a spin carrier can be reversed, and simultaneously an applied external electric field drives the charge-reversed spin carrier to move in the opposite direction. As for a spinless carrier, the photoexcitation dissociates it into two spin carriers, forming entanglement. The coupling between the newly produced spin carriers and a ferromagnet will change the magnetoresistance. By combining an electric field, magnetic field and photoexcitation, two generic optically-controlled ultrafast response organic spin valves are designed.

Optical properties of ZnO/MgZnO quantum well (QW) structures, considering piezoelectric and spontaneous polarizations, are investigated by using the non-Markovian gain model with many-body effects. The spontaneous polarization constant for MgO was determined from a comparison with the experiment, which gives a value of about −0.070 C/m². The optical matrix element of the ZnO/MgZnO QW structure decreases with the inclusion of Mg. This is attributed to an increase in the spatial separation between the electron and the hole wave functions due to the large internal field. However, the ZnO/MgZnO QW structure with a relatively high Mg composition (x = 0.3) is found to have a larger optical gain than that with a relatively low Mg composition. This can be explained by the fact that the quasi-Fermi-level separation ΔE_fc in the conduction band increases with the inclusion of Mg. The increase in ΔE_fc is because the QW structure with a high Mg composition has a larger energy spacing in the conduction band. We also know that the exciton binding energy of ZnO/MgZnO QW structures is much larger than that of GaN/AlGaN QW structures. This can be explained by the fact that ZnO/MgZnO QW structures have a larger matrix element than the GaN/AlGaN QW structures and by the smaller dielectric constant.

Titanium dioxide is one of the most widely investigated oxides. This is due to its broad range of applications, from catalysis to photocatalysis to photovoltaics. Despite this large interest, many of its bulk properties have been sparsely investigated using either experimental techniques or ab initio theory. Further, some of TiO₂'s most important properties, such as its electronic band gap, the localized character of excitons, and the localized nature of states induced by oxygen vacancies, are still under debate. We present a unified description of the properties of rutile and anatase phases, obtained from ab initio state of the art methods, ranging from density functional theory (DFT) to many body perturbation theory (MBPT) derived techniques. In so doing, we show how advanced computational techniques can be used to quantitatively describe the structural, electronic, and optical properties of TiO₂ nanostructures, an area of fundamental importance in applied research. Indeed, we address one of the main challenges to TiO₂-photocatalysis, namely band gap narrowing, by showing how to combine nanostructural changes with doping. With this aim we compare TiO₂'s electronic properties for 0D clusters, 1D nanorods, 2D layers, and 3D bulks using different approximations within DFT and MBPT calculations. While quantum confinement effects lead to a widening of the energy gap, it has been shown that substitutional doping with boron or nitrogen gives rise to (meta-)stable structures and the introduction of dopant and mid-gap states which effectively reduce the band gap. Finally, we report how ab initio methods can be applied to understand the important role of TiO₂ as electron-acceptor in dye-sensitized solar cells. This task is made more difficult by the hybrid organic-oxide structure of the involved systems.

The feasibility of tailoring of optical and nonlinear-optical properties of negative-index nanocomposites with control lasers as well as the feasibility of the design of novel photonic microdevices and all-optical data processing chips are shown and proved with numerical simulations.

When an electric dipole moment rotates, the flow pattern of the emitted energy exhibits a vortex structure in the near field. The field lines of energy flow swirl around an axis which is perpendicular to the plane of rotation of the dipole. This rotation leads to an apparent shift of the dipole when viewed from the far field. The shift is of the order of the spatial extend of the vortex, which is about a fraction of an optical wavelength. We also show that when an image of the radiation is formed on an observation plane in the far field, the rotation of the field lines in the near field leads to a shift of the dipole image.

This chapter presents an overview of laser-induced femtosecond magnetism. We first review some basic elements in femtomagnetism and then explain the roles of exchange interaction and spin-orbit coupling. Finally, we summarize our current understanding.

A promising avenue in the development of high-energy pulsed chemical HF/DF lasers and amplifiers is the utilization of a photon-branched chain reaction initiated in a two-phase active medium, i.e., a medium containing a laser working gas and ultradispersed passivated metal particles. These particles are evaporated under the action of IR laser radiation, resulting in the appearance of free atoms, their diffusion into the gas, and the development of a photon-branching chain process, which involves photons as both reactants and products. The key obstacle here is the formation a relatively-large volume (in excess of 10³ cm³) of the stable active medium and filling this volume homogeneously for a short time with a sub-micron monodispersed metal aerosol, which has specified properties. In this chapter, results are presented for an extensive study of laser initiation of a photon-branched chain reaction in a gas-dispersed H₂-F₂ medium.

The calculation of transport coefficients, such as thermal conductivity and first viscosity, in dilute ³He-⁴He mixtures is reviewed. Besides phonon-³He scattering processes, the effects of three-phonon processes, which are the dominant scattering mechanism for liquid ⁴He at low temperatures, are included.

Structure prediction of crystalline compounds using unbiased search methods remains a challenging task at the forefront of materials science. An ability to predict ground state structures as well as temperature and pressure dependent polymorphs without experimental input is not generally possible in all classes of materials. However, significant advances have been made in subclasses of materials where simplified Hamiltonians allow rapid searching of the configurational potential energy surface without the need for density functional theory or more complicated electronic structure methods. We review a novel method of structure prediction for ionic compounds consisting of a collection of charge balanced cations and complex anions based on prototype electrostatic ground states (PEGS). This method, used in concert with database search methods, is shown to successfully predict many experimentally observed crystal structures, and complicated reaction pathways for materials used in advanced hydrogen storage compounds.

The following sections are included:

• Index

• About the Editors