Warm dense matter is the state between the heated condensed matter and plasma. The importance of the development of warm dense matter theoretical description is determined by the fact that such conditions may arise in the variety of different scientific and industrial applications. For instance, warm dense matter is formed: in the matter impacted by femto‐ and picoseconds laser pulses; in nuclear materials at the formation of radiation track, etc. In these phenomena, the initial state of the system is a two‐temperature state and the electron temperature may be several orders higher than the ion one. In this work, the attempt of development of the united atomistic model of a warm dense matter is carried out. The special consideration is given to the twotemperature effects and the influence of the electron pressure on the behavior of ions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A graphene nanobubble consists of a graphene sheet, an atomically flat substrate, and a substance enclosed between them. Unlike conventional confinement with rigid walls and a fixed volume, the graphene nanobubble has one stretchable wall, which is the graphene sheet, and its volume can be adjusted by changing the shape. In this study, we developed a model of a graphene nanobubble based on classical density functional theory and the elastic theory of membranes. The proposed model takes into account the inhomogeneity of the enclosed substance, the nonrigidity of the wall, and the alternating volume. As an example application, we utilize the developed model to investigate fluid argon inside graphene nanobubbles at room temperature. We observed a constant height-to-radius ratio over the whole range of radii considered, which is in agreement with the results from experiments and molecular dynamics simulations. The developed model provides a theoretical tool to study both the inner structure of the confined substance and the shape of the graphene nanobubble. The model can be easily extended to other types of nonrigid confinement.
Density functional theory (DFT) is one of the most widely used tools to solve the many-body Schrodinger equation. The core uncertainty inside DFT theory is the exchange-correlation (XC) functional, the exact form of which is still unknown. Therefore, the essential part of DFT success is based on the progress in the development of XC approximations. Traditionally, they are built upon analytic solutions in low- and high-density limits and result from quantum Monte Carlo numerical calculations. However, there is no consistent and general scheme of XC interpolation and functional representation. Many different developed parametrizations mainly utilize a number of phenomenological rules to construct a specific XC functional. In contrast, the neural network (NN) approach can provide a general way to parametrize an XC functional without any a priori knowledge of its functional form. In this work, we develop NN XC functionals and prove their applicability to 3-dimensional physical systems. We show that both the local density approximation (LDA) and generalized gradient approximation (GGA) are well reproduced by the NN approach. It is demonstrated that the local environment can be easily considered by changing only the number of neurons in the first layer of the NN. The developed NN XC functionals show good results when applied to systems that are not presented in the training/test data. The generalizability of the formulated NN XC framework leads us to believe that it could give superior results in comparison with traditional XC schemes provided training data from high-level theories such as the quantum Monte Carlo and post-Hartree-Fock methods.
Warm dense matter conductivity and reflectivity are investigated by means of density functional theory. Both one‐ and two‐temperature cases are considered. One‐temperature mode is related to equilibrium state where temperature of electrons and ions are equal. As an example of one‐temperature system xenon plasma is studied. The reflectivity of shock‐compressed dense xenon plasma is calculated and compared with experimental data. Two‐temperature mode is associated with different temperature of electrons and ions. The thermal conductivity of aluminium and gold in such mode is examined. The comparison of obtained results with theoretical model based on Boltzmann equation is conducted. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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