MatD^3^: A Database and Online Presentation Package for Research Data Supporting Materials Discovery, Design, and Dissemination

The discovery of new materials as well as the determination of a vast set of materials properties for science and technology is a fast growing field of research, with contributions from many groups worldwide. Materials data from individual research groups is traditionally disseminated by means of loosely interconnected, peer-reviewed publications. MatD3 is an open-source, dedicated database and web application framework designed to store, curate and disseminate experimental and theoretical materials data generated by individual research groups or research consortia. A research group can set up its own instance of MatD3 and publish scientific results or simply use an existing online MatD3 instance. Disseminating research data in this form enables broader access, reproducibility, and repurposing of scientific products. MatD3 is a general purpose database that does not focus on any specific level of theory or experimental method. Instead, the focus is on storing and making accessible the data and making it straightforward to curate them

ELSI -- An open infrastructure for electronic structure solvers

Routine applications of electronic structure theory to molecules and periodic systems need to compute the electron density from given Hamiltonian and, in case of non-orthogonal basis sets, overlap matrices. System sizes can range from few to thousands or, in some examples, millions of atoms. Different discretization schemes (basis sets) and different system geometries (finite non-periodic vs. infinite periodic boundary conditions) yield matrices with different structures. The ELectronic Structure Infrastructure (ELSI) project provides an open-source software interface to facilitate the implementation and optimal use of high-performance solver libraries covering cubic scaling eigensolvers, linear scaling density-matrix-based algorithms, and other reduced scaling methods in between. In this paper, we present recent improvements and developments inside ELSI, mainly covering (1) new solvers connected to the interface, (2) matrix layout and communication adapted for parallel calculations of periodic and/or spin-polarized systems, (3) routines for density matrix extrapolation in geometry optimization and molecular dynamics calculations, and (4) general utilities such as parallel matrix I/O and JSON output. The ELSI interface has been integrated into four electronic structure code projects (DFTB+, DGDFT, FHI-aims, SIESTA), allowing us to rigorously benchmark the performance of the solvers on an equal footing. Based on results of a systematic set of large-scale benchmarks performed with Kohn–Sham density-functional theory and density-functional tight-binding theory, we identify factors that strongly affect the efficiency of the solvers, and propose a decision layer that assists with the solver selection process. Finally, we describe a reverse communication interface encoding matrix-free iterative solver strategies that are amenable, e.g., for use with planewave basis sets. Program summary: Program title: ELSI Interface CPC Library link to program files: http://dx.doi.org/10.17632/473mbbznrs.1 Licensing provisions: BSD 3-clause Programming language: Fortran 2003, with interface to C/C++ External routines/libraries: BLACS, BLAS, BSEPACK (optional), EigenExa (optional), ELPA, FortJSON, LAPACK, libOMM, MPI, MAGMA (optional), MUMPS (optional), NTPoly, ParMETIS (optional), PETSc (optional), PEXSI, PT-SCOTCH (optional), ScaLAPACK, SLEPc (optional), SuperLU_DIST Nature of problem: Solving the electronic structure from given Hamiltonian and overlap matrices in electronic structure calculations. Solution method: ELSI provides a unified software interface to facilitate the use of various electronic structure solvers including cubic scaling dense eigensolvers, linear scaling density matrix methods, and other approaches

Ergastatud seisundite dünaamika kõrge ergastustiheduse tingimustes volframaatides

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Volframaadi kristallid on laialdaselt kasutuses stsintillaatoritena ioniseeriva kiirguse detekteerimisel. Näiteks omavad nad rakendusi meditsiinilistes uuringutes, turvasüsteemides ja kõrge energia füüsikas. Selleks, et parandada stsintillaatorite efektiivsust, on oluline omada võimalikult täpset ettekujutust nende stsintillatsiooni mehhanismidest. See puudutab näiteks stsintillaatori mitteproportsionaalset kostet, mis on üks tõsisemaid seni lahendamata probleeme stsintillaatorite jaoks. Mitteproportsionaalsus tähendab, et stsintillatsiooni footonite arv ei ole proportsionaalne neelatava kõrge energiaga osakese energiaga. Tulemuseks on stsintilaatori energeetilise lahutusvõime märgatav halvenemine. Antud töös uuritakse nii teoreetiliste kui eksperimentaalsete vahenditega ergastatud seisundite dünaamikat, mis on osa stsintillatsiooni protsessist. Arendatakse mitmeid mudeleid kirjeldamaks ergastuse, termilisatsiooni ja luminestsentsi staadiume. Mudeleid rakendatakse edukalt valitud volframaadi kristallide peal. Töö oluliseimaks tulemuseks võib lugeda mitteproportsionaalsuse täpse mudeli väljatöötamist, mis põhineb dipool-dipool interaktsioonil eksitonide vahel ja on rakendatav eksitonkiirgusel põhinevate stsintillaatorite jaoks.Tungstate crystals are widely used as scintillators for the detection of ionizing radiation, with applications ranging from medical imaging to security systems to high energy physics. In order to improve the efficiency of scintillators, a better understanding of their scintillation mechanisms is required. This includes the phenomenom of scintillator nonproportionality, which is one of the major unsolved problems for scintillators. Nonproportionality means that the total light output of the scintillator is not proportional to the energy of the absorbed high-energy particle and leads to a considerable worsening of the energy resolution. This work includes the theoretical and experimental investigation of the excited state dynamics that constitute the scintillation process. We develop several models describing the excitation, thermalization, and the luminescence stage. The models are successfully tested on experimental data obtained for the selected tungstate crystals. Most importantly, we are able to provide an accurate description of nonproportionality, which is based on the dipole-dipole interaction of excitons and is applicable to excitonic intrinsic scintillators

Long-Lived ¹³C₂ Nuclear Spin States Hyperpolarized by Parahydrogen in Reversible Exchange at Microtesla Fields

Parahydrogen is an inexpensive and readily available source of hyperpolarization used to enhance magnetic resonance signals by up to four orders of magnitude above thermal signals obtained at ∼10 T. A significant challenge for applications is fast signal decay after hyperpolarization. Here we use parahydrogen-based polarization transfer catalysis at microtesla fields (first introduced as SABRE-SHEATH) to hyperpolarize ¹³C₂ spin pairs and find decay time constants of 12 s for magnetization at 0.3 mT, which are extended to 2 min at that same field, when long-lived singlet states are hyperpolarized instead. Enhancements over thermal at 8.5 T are between 30 and 170 fold (0.02 to 0.12% polarization). We control the spin dynamics of polarization transfer by choice of microtesla field, allowing for deliberate hyperpolarization of either magnetization or long-lived singlet states. Density functional theory calculations and experimental evidence identify two energetically close mechanisms for polarization transfer: First, a model that involves direct binding of the ¹³C₂ pair to the polarization transfer catalyst and, second, a model transferring polarization through auxiliary protons in substrates

The ELSI Infrastructure for Scalable Electronic Structure Theory

Lightning talk accompanying the poster describing the ELSI infrastructure in detail.<br