We examined the estimation of thermal conductivity through molecular dynamics simulations for a superionic conductor, α-Ag2Se, using the interatomic potential based on an artificial neural network (ANN potential). The training data were created using the existing empirical potential of Ag2Se to help find suitable computational and training requirements for the ANN potential, with the intent to apply them to first-principles calculations. The thermal conductivities calculated using different definitions of heat flux were compared, and the effect of explicit long-range Coulomb interaction on the conductivities was investigated. We clarified that using a rigorous heat flux formula for the ANN potential, even for highly ionic α-Ag2Se, the resulting thermal conductivity was reasonably consistent with the reference value without explicitly considering Coulomb interaction. It was found that ANN training including the virial term played an important role in reducing the dependency of thermal conductivity on the initial values of the weight parameters of the ANN.

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Some laboratory tests showed rather strange hysteresis loops in strain-temperature space, where the strains were measured with a strain gauge on the surface of a wet cubic rock sample under a subzero temperature cycle. This report gives introductory remarks and the first result on a new project launched by the present authors. The project is intended to make clear the major mechanisms responsible for the unexpected hysteresis loops in the strain-temperature diagram, in which an abrupt increase in strains appeared at a halfway point of the cooling process at higher cooling rates. The hysteresis loops suggest that various thermal and mechanical (or physical) phenomena take place within the rock sample; some possible candidates of causes behind the phenomena are discussed and a hypothesis associated with them is proposed. Furthermore, to separate an unexpected part of the hysteresis loop from its ''regular'' part, thermal strains on the surface of a spherical sample under a temperature cycle are calculated within the framework of linear thermoelasticity. The equivalence between strains on the surface of a cubic sample and that of a spherical one is discussed.