Aftershocks following crash of currency exchange rate: The case of RUB/USD in 2014

The dynamical behavior of the currency exchange rate after its large-scale catastrophe is discussed through a case study of the rate of Russian rubles to US dollars after its crash in 2014. It is shown that, similarly to the case of the stock market crash, the relaxation is characterized by a power law, which is in analogy with the Omori-Utsu law for earthquake aftershocks. The waiting-time distribution is found to also obey a power law. Furthermore, the event-event correlation is discussed, and the aging phenomenon and scaling property are observed. Comments are made on (non-)Markovianity of the aftershock process and on a possible relevance of glassy dynamics to the market system after the crash.Comment: 17 pages, 6 figures. The title changed. Published versio

Non-collinear Magnetic Atomic Cluster Expansion for Iron

The Atomic Cluster Expansion (ACE) provides a formally complete basis for the local atomic environment. ACE is not limited to representing energies as a function of atomic positions and chemical species, but can be generalized to vectorial or tensorial properties and to incorporate further degrees of freedom (DOF). This is crucial for magnetic materials with potential energy surfaces that depend on atomic positions and atomic magnetic moments simultaneously. In this work, we employ the ACE formalism to develop a non-collinear magnetic ACE parametrization for the prototypical magnetic element Fe. The model is trained on a broad range of collinear and non-collinear magnetic structures calculated using spin density functional theory. We demonstrate that the non-collinear magnetic ACE is able to reproduce not only ground state properties of various magnetic phases of Fe but also the magnetic and lattice excitations that are essential for a correct description of the finite temperature behavior and properties of crystal defects.Comment: 19 pages, 20 figures, 2 table

Automated free-energy calculation from atomistic simulations

We devise automated workflows for the calculation of Helmholtz and Gibbs free energies and their temperature and pressure dependence and provide the corresponding computational tools. We employ nonequilibrium thermodynamics for evaluating the free energy of solid and liquid phases at a given temperature and reversible scaling for computing free energies over a wide range of temperatures, including the direct integration of P−T coexistence lines. By changing the chemistry and the interatomic potential, alchemical and upscaling free energy calculations are possible. Several examples illustrate the accuracy and efficiency of our implementation

Initial steps in reactions of aquathermolysis of cyclohexyl phenyl sulfide by means of ab initio calculations

Aquathermolysis is often proposed as a method to reduce the viscosity of heavy oils. In the present work we have investigated the aquathermolysis reaction of cyclohexyl phenyl sulfide in water medium by means of density functional theory. The water molecule was considered as a reagent and as a catalyst. We have shown that ab initio quantum chemistry methods could be applicable for comparative analysis of chemical reaction pathways in aquathermolysis processes. The obtained results could be useful for the systems like tert-alkyl (secondary-alkyl) thiophenyl ethers, which could be formed in heavy oils at harsh conditions. The scheme of different reaction directions with corresponding calculated values of reaction barriers, which are correlated with experimental data, is presented and could be used for comparison with other reaction mechanisms