Understanding the difference in cohesive energies between alpha and beta tin in DFT calculations

The transition temperature between the low-temperature alpha phase of tin to beta tin is close to the room temperature (Tab =13C), and the difference in cohesive energy of the two phases at 0 K of about dEcoh=0.02 eV/atom is at the limit of the accuracy of DFT (density functional theory) with available exchange-correlation functionals. It is however critically important to model the relative phase energies correctly for any reasonable description of phenomena and technologies involving these phases, for example, the performance of tin electrodes in electrochemical batteries. Here, we show that several commonly used and converged DFT setups using the most practical and widely used PBE functional result in dEcoh of about 0.04 eV/atom, with different types of basis sets and with different models of core electrons (all-electron or pseudopotentials of different types), which leads to a significant overestimation of Tab. We show that this is due to the errors in relative positions of s and p -like bands, which, combined with different populations of these bands in alpha and beta Sn, leads to overstabilization of alpha tin. We show that this error can be effectively corrected by applying a Hubbard +U correction to s -like states, whereby correct cohesive energies of both alpha and beta Sn can be obtained with the same computational scheme. We quantify for the first time the effects of anharmonicity on dEcoh and find that it is negligible.Comment: 7 pages, 5 figure

Aluminum doping improves the energetics of lithium, sodium, and magnesium storage in silicon

While Si is an effective insertion type anode for Li-ion batteries, crystalline Si has been shown to be unsuitable for Na and Mg storage due, in particular, to insufficient binding strength. It has recently been reported that Si nanowires could be synthesized with high-concentration (several atomic %) and dispersed Al doping. Here we show based on density functional theory calculations that Al doping significantly improves the energetics for Na and Mg insertion, specifically, making it thermodynamically favored versus vacuum reference states. For high Al concentrations, the energy of Mg in Al-doped Si approaches the cohesive energy of Mg. However, the migration barriers for the diffusion of Li (0.57-0.70 eV), Na (1.07-1.19 eV) and Mg (0.97-1.18 eV) in Al-doped Si are found to remain about as high as in pure Si, likely preventing effective electrochemical sodiation and magnesiation

Refinancing as a tool for maintaining the liquidity of banking institutions of Ukraine

Розкрито особливості рефінансування вітчизняних банків Національним банком України, визначено різні способи його проведення, досліджено значення цього монетарного інструменту в реалізації грошово-кредитної політики центрального банку та виконанні ним функції кредитора останньої інстанції з метою підтримки ліквідності банків на необхідному рівні в умовах стабільного розвитку економіки та за умов кризи. Наведено аналіз динаміки обсягів рефінансування банківських установ Національним банком України та середньозваженої процентної ставки за операціями рефінансування. Обґрунтовано пропозиції щодо удосконалення процесу рефінансування банків, які дозволять покращити його механізм і підвищити ефективність відповідно до потреб банків та економіки країниThe article reveals the features of refinancing of domestic banks by the National Bank of Ukraine; various ways of its prosecuting are also studied, the significance of this monetary tool in the marketing of monetary policy of the Central Bank and its function as a moneylender of last echelon to support the liquidity of banks on the desired level in the conditions of stable development of the economy and in the conditions of crisis is investigated. The analysis of changes in the amount of refinancing of banking institutions by the National Bank of Ukraine and the average weighted interest rate on refinancing operations is provided. The proposals for improving the process of refinancing of banks, which will improve its mechanism and efficiency, according to the needs of banks and the economy are grounded. Possible ways to improve banks' refinancing may be the introduction of a new type of refinancing - giving intraday credit; increasing types of providing loans refinancing, which will promote the development of refinancing instruments and activate the equity market in Ukraine; promoting the development of the equity market to a wider use of repo; enhancing the role of the discount rate and refinancing rates that will more quickly transform changes of the discount rate and refinancing rates into banks’ changes interest rates on loans and deposits, as well as rates in the interbank market; establishing clear criteria to determine with high accuracy the size of the required bank liquidity, adequate cycle and the state of the economy, which will help the banks receive the necessary amounts of refinancing loans and ensure their timely return; control implementation of the National Bank of Ukraine for the intended use of the bank loans obtained refinancing to facilitate channeling of funds received to maintain current liquidity or financing the real economy, and not for speculative transactions in the interbank market

Dopant-Dopant Interactions in Beryllium doped Indium Gallium Arsenide: an Ab Initio Study

We present an ab initio study of dopant-dopant interactions in beryllium-doped InGaAs. We consider defect formation energies of various interstitial and substitutional defects and their combinations. We find that all substitutional-substitutional interactions can be neglected. On the other hand, interactions involving an interstitial defect are significant. Specially, interstitial Be is stabilized by about 0.9/1.0 eV in the presence of one/two BeGa substitutionals. Ga interstitial is also substantially stabilized by Be interstitials. Two Be interstitials can form a metastable Be-Be-Ga complex with a dissociation energy of 0.26 eV/Be. Therefore, interstitial defects and defect-defect interactions should be considered in accurate models of Be doped InGaAs. We suggest that In and Ga should be treated as separate atoms and not lumped into a single effective group III element, as has been done before. We identified dopant-centred states which indicate the presence of other charge states at finite temperatures, specifically, the presence of Beint+1 (as opposed to Beint+2 at 0K)

The loss of the property of locality of the kernel in high-dimensional Gaussian process regression on the example of the fitting of molecular potential energy surfaces

Kernel based methods including Gaussian process regression (GPR) and generally kernel ridge regression (KRR) have been finding increasing use in computational chemistry, including the fitting of potential energy surfaces and density functionals in high-dimensional feature spaces. Kernels of the Matern family such as Gaussian-like kernels (basis functions) are often used, which allows imparting them the meaning of covariance functions and formulating GPR as an estimator of the mean of a Gaussian distribution. The notion of locality of the kernel is critical for this interpretation. It is also critical to the formulation of multi-zeta type basis functions widely used in computational chemistry We show, on the example of fitting of molecular potential energy surfaces of increasing dimensionality, the practical disappearance of the property of locality of a Gaussian-like kernel in high dimensionality. We also formulate a multi-zeta approach to the kernel and show that it significantly improves the quality of regression in low dimensionality but loses any advantage in high dimensionality, which is attributed to the loss of the property of locality

Conceptual approaches towards interpretation of anti-crisis management economic essence

Виокремлено концептуальні підходи вітчизняних та зарубіжних авторів до трактування економічної сутності антикризового менеджменту. На підставі проведення ретроспективного аналізу встановлено причини появи та розвитку антикризового менеджменту як одного із функціональних напрямів управління організацією. Визначено, що зарубіжні та вітчизняні економісти не вступають у протиріччя щодо трактування сутності антикризового менеджменту, а лише доповнюють один одного, розширюючи та синтезуючи його проблематику. Обґрунтовано, що антикризовий менеджмент необхідно розглядати як постійно діючий специфічний вид управління, спрямований на попередження можливих ускладнень у діяльності системи, нейтралізацію кризових явищ і забезпечення її подальшого функціонування та розвитку шляхом вчасної реалізації адекватних управлінських рішень й ефективного використання внутрішніх ресурсів.Conceptual approaches of domestic and foreign scientists towards interpretation of anti-crisis management economic essence based on the investigations systematization are identified in the paper. The reasons of anti-crisis management appearance and development as one of functional directions of organizations management are determined according to retrospective analysis. It identifies that domestic and foreign economists are not in contradiction towards interpretation of anti-crisis management economic essence, but complement each other by extending and synthesizing its range of problems. The necessity of anti-crisis management to be considered as a constantly acting specific type of management, which is directed on possible difficulties prevention, neutralization of crisis trends and provision of its further functioning and development with the help of in-time realization of adequate administrative decisions and efficient usage of internal resources is substantiated. Depending on the stage and depth of crisis, it is determined that anti-crisis management is divided into the following types: pre-crisis (preventative – provides the system of prophylactic actions aimed at imbalance recovery, costs minimization, competitiveness); crisis (management in conditions of crisis, directed on stabilization the crisis situation assessment, determination of crisis factors, investigation of economic system strengths and weaknesses, assessment of crisis overcoming potential, search for solutions of negative trends minimization, financial sustainability recovery); post-crisis (directed on overcoming the crisis negative results and return to pre-crisis activity parameters, provides justification and realization of crisis overcoming strategic program, operative identification of program realization of actual results deviation and designation of system of actions of crisis negative trends elimination)