## Abstract

Recent density functional theory simulations showed that metals have a hitherto overlooked symmetry termed

“hidden scale invariance” [Hummel et al., Phys. Rev. B 92, 174116 (2015)]. This scaling property implies

the existence of lines in the thermodynamic phase diagram, so-called isomorphs, along which structure and

dynamics are invariant to a good approximation when given in properly reduced units. This means that the phase

diagram becomes effectively one-dimensional with regard to several physical properties. This paper investigates

consequences and implications of the isomorph theory in six metallic crystals: Au, Ni, Cu, Pd, Ag, and Pt. The

data are obtained from molecular dynamics simulations employing many-body effective medium theory (EMT)

to model the atomic interactions realistically. We test the predictions from isomorph theory for structure and

dynamics by means of the radial distribution and the velocity autocorrelation functions, as well as the prediction

of instantaneous equilibration after a jump between two isomorphic state points. Many properties of crystals tend

to be dominated by defects, and many of the properties associated with these defects are expected to be isomorph

invariant as well. This is investigated in this paper for the case of vacancy diffusion. In regard to the perfect crystal

properties, we find the predicted invariance of structure and also, though less perfectly, of dynamics. We show

results on the variation of the density-scaling exponent γ , which can be related to the Grüneisen parameter, for all

six metals.We consider large density changes up to a factor of two, corresponding to very high pressures. Unlike

systems modeled using the Lennard-Jones potential where the density-scaling exponent γ is almost constant,

this quantity varies substantially when using the EMT potential and is also strongly material dependent.

“hidden scale invariance” [Hummel et al., Phys. Rev. B 92, 174116 (2015)]. This scaling property implies

the existence of lines in the thermodynamic phase diagram, so-called isomorphs, along which structure and

dynamics are invariant to a good approximation when given in properly reduced units. This means that the phase

diagram becomes effectively one-dimensional with regard to several physical properties. This paper investigates

consequences and implications of the isomorph theory in six metallic crystals: Au, Ni, Cu, Pd, Ag, and Pt. The

data are obtained from molecular dynamics simulations employing many-body effective medium theory (EMT)

to model the atomic interactions realistically. We test the predictions from isomorph theory for structure and

dynamics by means of the radial distribution and the velocity autocorrelation functions, as well as the prediction

of instantaneous equilibration after a jump between two isomorphic state points. Many properties of crystals tend

to be dominated by defects, and many of the properties associated with these defects are expected to be isomorph

invariant as well. This is investigated in this paper for the case of vacancy diffusion. In regard to the perfect crystal

properties, we find the predicted invariance of structure and also, though less perfectly, of dynamics. We show

results on the variation of the density-scaling exponent γ , which can be related to the Grüneisen parameter, for all

six metals.We consider large density changes up to a factor of two, corresponding to very high pressures. Unlike

systems modeled using the Lennard-Jones potential where the density-scaling exponent γ is almost constant,

this quantity varies substantially when using the EMT potential and is also strongly material dependent.

Originalsprog | Engelsk |
---|---|

Artikelnummer | 022142 |

Tidsskrift | Physical Review E |

Antal sider | 13 |

ISSN | 2470-0045 |

DOI | |

Status | Udgivet - 27 feb. 2019 |