Electronic stopping power from first-principles calculations with account for core electron excitations and projectile ionization

We use Ehrenfest dynamics and time-dependent density functional theory to calculate electronic stopping power Se of energetic ions in graphitic targets from first principles. By treating core electrons as valence electrons within the projected augmented wave framework, we demonstrate that this approach provides an accurate description of Se for a wide range of ions and ion energies, even when not only valence, but also core electron excitations are essential. Our impact-parameter-dependent approach capable of describing the stopping of both low- and high-energy ions is a significant step forward in Se calculations, as it makes it possible to monitor projectile charge state during impacts, estimate contributions of core and valence electron excitations to Se, and it gives a quantitative description of electronic stopping in the cross-over region for bulk solids and nanostructures from first principles.Peer reviewe

Nonadiabatic Ehrenfest molecular dynamics within the projector augmented-wave method

We have derived equations for nonadiabatic Ehrenfest molecular dynamics which conserve the total energy in the case of time-dependent discretization for electrons. A discretization is time-dependent in all cases where it or part of it depends on the positions of the nuclei, for example, in atomic orbital basis sets, and in the projector augmented-wave (PAW) method, where the augmentation functions depend on the nuclear positions. We have derived, implemented, and analyzed the energy conserving equations and their most common approximations for a 1D test system where we can achieve numerical results converged to a high accuracy. Based on the observations in 1D, we implement and analyze the Ehrenfest molecular dynamics in 3D using the PAW method and the time-dependent density functional formalism. We demonstrate the applicability of our method by carrying out calculations for small and medium sized molecules in both the adiabatic and the nonadiabatic regime.Comment: 12 pages, 10 figure

QuantumATK: An integrated platform of electronic and atomic-scale modelling tools

QuantumATK is an integrated set of atomic-scale modelling tools developed since 2003 by professional software engineers in collaboration with academic researchers. While different aspects and individual modules of the platform have been previously presented, the purpose of this paper is to give a general overview of the platform. The QuantumATK simulation engines enable electronic-structure calculations using density functional theory or tight-binding model Hamiltonians, and also offers bonded or reactive empirical force fields in many different parametrizations. Density functional theory is implemented using either a plane-wave basis or expansion of electronic states in a linear combination of atomic orbitals. The platform includes a long list of advanced modules, including Green's-function methods for electron transport simulations and surface calculations, first-principles electron-phonon and electron-photon couplings, simulation of atomic-scale heat transport, ion dynamics, spintronics, optical properties of materials, static polarization, and more. Seamless integration of the different simulation engines into a common platform allows for easy combination of different simulation methods into complex workflows. Besides giving a general overview and presenting a number of implementation details not previously published, we also present four different application examples. These are calculations of the phonon-limited mobility of Cu, Ag and Au, electron transport in a gated 2D device, multi-model simulation of lithium ion drift through a battery cathode in an external electric field, and electronic-structure calculations of the composition-dependent band gap of SiGe alloys.Comment: Submitted to Journal of Physics: Condensed Matte

Added Value of Vaisala AQT530 Sensors as a Part of a Sensor Network for Comprehensive Air Quality Monitoring

Poor air quality influences the quality of life in the urban environment. The regulatory observation stations provide the backbone for the city administration to monitor urban air quality. Recently a suite of cost-effective air quality sensors has emerged to provide novel insights into the spatio-temporal variability of aerosol particles and trace gases. Particularly in low concentrations these sensors might suffer from issues related e.g., to high detection limits, concentration drifts and interdependency between the observed trace gases and environmental parameters. In this study we characterize the optical particle detector used in AQT530 (Vaisala Ltd.) air quality sensor in the laboratory. We perform a measurement campaign with a network of AQT530 sensors in Helsinki, Finland in 2020-2021 and present a long-term performance evaluation of five sensors for particulate (PM10, PM2.5) and gaseous (NO2, NO, CO, O-3) components during a half-year co-location study with reference instruments at an urban traffic site. Furthermore, short-term (3-5 weeks) co-location tests were performed for 25 sensors to provide sensor-specific correction equations for the fine-tuning of selected pollutants in the sensor network. We showcase the added value of the verified network of 25 sensor units to address the spatial variability of trace gases and aerosol mass concentrations in an urban environment. The analysis assesses road and harbor traffic monitoring, local construction dust monitoring, aerosol concentrations from fireworks, impact of sub-urban small scale wood combustion and detection of long-range transport episodes on a city scale. Our analysis illustrates that the calibrated network of Vaisala AQT530 air quality sensors provide new insights into the spatio-temporal variability of air pollution within the city. This information is beneficial to, for example, optimization of road dust and construction dust emission control as well as provides data to tackle air quality problems arising from traffic exhaust and localized wood combustion emissions in the residential areas.Peer reviewe

Ei-adiabaattinen kytkettyjen elektronien ja ionien dynamiikka

Excited electronic states are quite common in nature. Phenomena related to excited states and their time development include light absorption, fluorescence, respiration and ignition of chemical reactions. Moreover, many experimental are based on activating the electron-ion system to excited states for detection. Consequently, a proper description of the excited electron-ion system and the related dynamical processes is crucial for the understanding of many natural processes. However, simulating coupled nonadiabatic electron-ion motion represents major computational challenges due to the computational demands and the difficulties in describing excited state wave functions accurately. Standard ab initio molecular dynamics (AIMD) schemes, which are based on the assumption that the dynamics is governed by a single electronic potential energy surface (PES), have been successfully used for studying a variety of dynamical processes in materials. However, this approach is severely limited when nonadiabatic processes that involve multiple potential energy surfaces are studied. Recently, the nonadiabatic MD technique called Ehrenfest molecular dynamics, in conjunction with the time-dependent density functional theory (TDDFT), has gained significant attention because it offers a computationally affordable approach to studying nonadiabatic processes. In this thesis, we implemented Ehrenfest MD in three different cases: 1) a one-dimensional model system with a simplified Hamiltonian, 2) three-dimensional systems using norm-conserving HGH pseudpopotentials and 3) three-dimensional systems using the PAW method. In cases 2) and 3), Ehrenfest MD was implemented in the electronic structure program GPAW, whereas for the 1D implementation, we developed a program with moving basis functions. In order to test the implementations, the dynamics of certain small molecules was studied. The GPAW simulations showed that the HGH implementation is successful in all aspects. Nuclear dynamics converged fast in all test cases, and total energy was well conserved in both adiabatic and nonadiabatic cases. In the simulations with the PAW method, however, total energy conservation problems were observed. Moreover, the 1D model was found to be a successful tool for simulating the PAW method. As we observed similar problems in 1D than in the PAW calculations, further research is required to gain a full understand of Ehrenfest MD with moving basis functions.Luonnossa esiintyy monia ilmiöitä, jotka liittyvät virittyneisiin tiloihin ja niiden aikakehitykseen. Tällaisia ilmiöitä ovat muiden muassa valon absorptio, fluoriloiste ja kemiallisten reaktioiden alkuvaiheet. Lisäksi monet kokeelliset menetelmät perustuvat tutkittavan elektroni-ioni-systeemin virittämiseen havaintoja varten. Näin ollen virittyneen elektroni-ioni-systeemin ja siihen liittyvien dynaamisten prosessien tarkka mallintaminen on keskeistä, jotta voidaan ymmärtää monia luonnollisia prosesseja ja tulkita kokeellista dataa. Ei-adiabaattisen dynamiikan mallintaminen on kuitenkin laskennallisesti erittäin haastavaa, sillä virittyneiden tilojen aaltofunktioiden kuvaaminen on vaikeaa, ja laskentatehoa vaaditaan paljon. Perinteisiä ab initio-molekyylidynamiikan menetelmiä, joissa oletetaan, että elektronit pysyvät perustilassa, eli virityksiä ei tapahdu, on menestyksekkäästi käytetty mitä erilaisimpien materiaaleissa esiintyvien dynaamisten prosessien tutkimiseen. Näitä menetelmiä ei kuitenkaan voi käyttää, kun tutkitaan ei-adiabaattisia prosesseja, joiden dynamiikassa on mukana useita potentiaalienergiapintoja. Viime aikoina ei-adiabaattisten prosessien mallintamiseen soveltuvan Ehrenfestin molekyylidynamiikkan käyttö yhdessä ajasta riippuvan tiheysfunktionaalitheorian kanssa on saanut merkittävää huomiota. Näin voidaan mallintaa ei-adiabaattisia prosesseja ilman, että laskentaresurssivaatimukset kasvavat kohtuuttomiksi. Tässä työssä toteutettiin Ehrenfestin molekyylidynamiikka kolmessa eri tapauksessa: 1) yksiulotteinen mallisysteemi yksinkertaistetulla Hamiltoniaanilla, 2) kolmiulotteiset systeemit, joissa käytetään HGH-pseudopotentiaaleja sekä 3) kolmiulotteiset systeemit, jossa käytetään PAW-menetelmää. Tapauksissa 2) ja 3) Ehrenfestin molekyylidynamiikka toteutettiin GPAW-elektronirakenneohjelmaan, kun taas yksiulotteinen toteutus tehtiin omaan ohjelmaan, jossa on liikkuvat kantafunktiot. Toteutusten testaamiseksi tutkittiin pienten molekyylien dynamiikkaa. GPAW-simulaatioissa havaittiin, että HGH-toteutus toimii kaikin puolin hyvin. Ydinten dynamiikka konvergoi nopeasti kaikissa testitapauksissa, ja kokonaisenergia säilyi hyvin sekä ei-adiabaattisissa että adiabaattisissa tapauksissa. PAW-menetelmällä tehdyissä simulaatioissa taas havaittiin ongelmia kokonaisenergian säilymisessä. Lisäksi yksiulotteisen ohjelman todettiin simuloivan hyvin PAW-menetelmää. Koska 1D-ohjelmassa havaittiin samankaltaisia ongelmia kuin PAW-laskuissa, vaaditaan jatkotutkimuksia Ehrenfestin molekyylidynamiikan kokonaisvaltaiseen ymmärtämiseen liikkuvilla kantafunktioilla

Sisältöyhteistyö kaupallisen televisioviihteen rahoituskeinona

Tässä opinnäytetyössä selvitetään, miten kumppaniyritykset osallistuvat kaupallisen television viihdeohjelmien tuotannon rahoitukseen ja sisältöön sekä millainen vaikutus sisältöyhteistyöllä on suomalaiseen viihdetelevisiotuotantoon. Teoriaosuudessa perehdytään sisältöyhteistyön määritelmään ja sen eri muotoihin. Tässä opinnäytetyössä sisältöyhteistyöllä viitataan ensisijaisesti brändien esiintymiseen televisio-ohjelman sisällössä. Teoriaosuudessa kerrotaan brändisijoittelun kehityksen keskeiset virstanpylväät, minkä lisäksi syvennytään brändinäkyvyyden vaikutuksiin ja tavoitteisiin katsojien mielikuvissa. Tutkimusosaan haastateltiin yhteensä yhdeksää yrityksen, kaupallisen kanavan ja tuotantoyhtiön työntekijää, jotka ovat työskennelleet merkittävässä asemassa sisältöyhteistyön avulla rahoitetuissa viihdeohjelmakumppanuuksissa. Tutkimus toteutettiin Delfoi-menetelmällä, jossa jokainen henkilö vastaa samoihin kysymyksiin anonyymisti. Ensimmäisen kyselykierroksen vastauksien analyysin pohjalta toteutettiin uusi, kohdistetumpi kyselykierros samoille henkilöille. Tutkimustuloksien pohjalta voidaan todeta, että kumppaniyrityksillä on kasvava rooli viihdeohjelmien rahoituksessa. Vastuu sisällöstä pysyy kuitenkin sisällöntekijöillä, vaikka kumppanin rahoitus olisi tuotannon kannalta ratkaiseva. Kokonaan kumppanien rahoittamien ohjelmien määrä lähitulevaisuudessa tulee jäämään vähäiseksi. Tärkeimmät suomalaisen sisältöyhteistyön laadun kehitykseen vaikuttavat tekijät ovat tuotantoihin sijoitetun budjetin suuruus sekä hyväksi havaittujen toimintatapojen vakiintuminen eri osapuolien välillä.This Bachelor's thesis studies how partner companies participate in the funding and creative processes of commercial entertainment television shows in Finland and how their involvement affects the Finnish television entertainment industry. This type of collaboration is known as content partnership. The theoretical part of this thesis focuses on the definition of content partnership and its different forms. In this thesis, content partnership generally refers to a brand placement in television programs. In addition, the thesis examines the evolution of the brand placement in audiovisual content and explains the effects and objectives of the branded content. A total of nine professionals from different partner companies, commercial channels and production companies were interviewed for the research. The selected experts have had a significant role in past content partnership productions. The research was conducted following the Delphi method where each person answers a questionnaire anonymously. After analyzing the first-round answers, another more specific set of questions was presented for the experts. Based on the results, the importance of partner companies as a funding and creative partner for commercial entertainment television shows is growing. Content creators will still be in charge of the content itself even if the partner companies' funding is crucial to the program's existence. Programs that are completely funded through partnerships will stay minimal in the near future. The most important development points for the Finnish content partnerships are the size of the television show's budget and establishing solid working methods among the parties involved

The Influence of Ignition Control Parameters on Combustion Stability and Spark plug Wear in a Large Bore Gas Engine

The paper presents novel studies on the impact of different ignition control parameters on combustion stability and spark plug wear. First, experimental results from a 32.4-liter biogas fueled large bore single cylinder spark ignition engine are discussed. Two different ignition systems were considered in the experiment: a DC inductive and an AC capacitive. The spark plugs used in the experiment were of dual-iridium standard J-gap design of different electrode gaps. Test results show the importance of different degrees of freedom to control a spark. A robust ignition is found to be achieved by using a very short spark duration, which in turn reduces total energy discharge at the gap. Further observations reveal that once a stable and self-propagating flame kernel is developed, it becomes independent of the spark energy further added to the gap. Finally, results from the spark plug wear tests using a pressurized rig chamber are discussed. It is found that an excessive spark energy discharge at the gap contributes to high erosion of spark plug electrodes, which is not desirable. However, spark energy is not the only factor affecting spark plug erosion. It is also the type of spark discharge (DC/AC) that governs the electrode wear over time. Therefore, the advantage of an AC spark discharge over a DC spark has been well established through the experimental results. The inherent property of an AC spark is found to be significantly slowing down electrode wear over time, hence increasing the service life of a spark plug