The Insulator-Metal Transition in Expanded Cesium

Ross, Marvin; Yang, Lin; Dahling, B. A.; Winter, N. W.

doi:10.1524/zpch.1994.184.part_1_2.065

Cited by 10 publications

(5 citation statements)

References 11 publications

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“…In the case of caesium the energy for dissociation of the dimer to free atoms is 0.43 eV. Total energy calculations [14] show that for densities near critical the energy separating a T = 0 K lattice of diatomic molecules and a monatomic bcc lattice has decreased to about 0.2 eV, and they have equal energies near twice the critical density. Since these structures represent two extremes of bonding we can expect that over this density range the dense fluid will retain these qualitative features and have a continuous spectrum of species with energies in the thermal range.…”

Section: The Two-state Vdw Modelmentioning

confidence: 98%

A modified Van der Waals model for the coexistence curve of expanded metals

Ross

Hensel

1996

J. Phys.: Condens. Matter

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Recent measurements for expanded Hg, Cs and Rb have shown that the liquidvapour coexistence curves for these metals do not obey the 'law of rectilinear diameters'. It is shown here that a two-state Van der Waals equation with a density-dependent cohesive energy will lead to compositional fluctuations that result in a breakdown of the 'law'. Calculations predict that Hg and the alkali metals will exhibit similar behaviour near the critical point. However, in the case of Hg the 6p-6s band-gap closure, which occurs at higher than critical densities, leads to an anomalous behaviour not observed in the alkali metals. The influence of this transition on the rectilinear behaviour is treated by introducing a further modification of the two-state model.

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Section: The Two-state Vdw Modelmentioning

confidence: 98%

A modified Van der Waals model for the coexistence curve of expanded metals

Ross

Hensel

1996

J. Phys.: Condens. Matter

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“…In order to get additional theoretical support for the suspected molecular species responsible for the observed pattern, exploratory calculations employing a simple model were undertaken: the total energy of expanded lattices for monatomic Rb and Rb 2 dimers at 0 K were carried out, using density functional theory (DFT) in the local density approximation (LDA) [84][85][86].…”

Section: The Expanded Liquid Metalmentioning

confidence: 99%

State dependent particle dynamics in liquid alkali metals

Pilgrim

Morkel

2006

J. Phys.: Condens. Matter

116

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This paper gives a survey of the particle dynamics in the liquid alkali metals observed with inelastic x-ray and neutron scattering experiments. Liquid rubidium and sodium are chosen as model fluids to represent the behaviour of this group of fluids. In the dense metallic monatomic melt the microscopic dynamics is characterized by collective excitations similar to those in the corresponding solids. The collective particle behaviour is appropriately described using a memory function formalism with two relaxation channels for the density correlation. A similar behaviour is found for the single particle motion where again two relaxation mechanisms are needed to accurately reproduce the experimental findings. Special emphasis is given to the density dependence of the particle dynamics. An interesting issue in liquid metals is the metal to non-metal transition, which is observed if the fluid is sufficiently expanded with increasing temperature and pressure. This causes distinct variations in the interparticle interactions, which feed back onto the motional behaviour. The associated variations in structure and dynamics are reflected in the shape of the scattering laws. The experimentally observed features are discussed and compared with simple models and with the results from computer simulations.

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“…DFT is a first principle quantum mechanical method for calculating total energies with the exchange and correlation terms written in terms of the local electron density (LDA). The computational method used here is the same as that reported previously for a similar set of calculations made for lattices of Cs and Cs 2 [18].…”

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Monatomic-Molecular Transition in Expanded Rubidium

et al. 1997

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S͑Q, v͒ for liquid rubidium measured along the liquid vapor coexistence line exhibits monatomic behavior from normal density down to twice the critical density. At this density we observe excitations characteristic of a harmonic oscillator. We interpret this as evidence for the passage of the fluid from a monatomic to a molecular state. First principle total energy calculations for lattices of ribidium at 0 K predict that expansion favors spin pairing and leads to a lattice of dimers with an increase in vibron energy with decreasing density. The excellent agreement of the calculated vibron energy with the experimental result provides theoretical support for the appearance of molecules.[S0031-9007(97)03149-9] PACS numbers: 61.25.Mv, 61.12.Ex, 64.70.Ja, 71.30. + h Liquid alkali metals at high densities close to their triple points can be regarded as monatomic fluids, where each atom contributes one single electron to a half-filled conduction band [1]. This view is consistent with several experimental observations: The dynamic structure factor S͑Q, v͒ for liquid rubidium measured at conditions close to the melting point exhibits distinct collective excitations at a high wave vector [2] typical for dense metallic fluids. The dispersion relation of these excitations is in accord with the result from computer simulations employing an interatomic pseudopotential typical for monatomic metals [3].Measurements of the static structure factor S͑Q͒ for fluid rubidium and cesium [4,5], carried out along the liquid vapor coexistence line for several densities between the melting point and the critical point, are consistent with this view. The main structural effect of the density decrease with increasing temperature is a reduction in the average number of nearest neighbors within the first coordination shell around an atom, while the mean interparticle distance remains nearly unchanged. This behavior changes dramatically if the metals are evaporated to the dilute gas phase close to their triple points. Under these conditions, alkali metal vapors behave like typical insulators with electrical conductivities less than 10 25 V 21 cm 21 [6]. Measurements of optical [7,8] and magnetic [9] properties and of equation of state data [8,10], as a function of density indicate that molecular aggregates such as dimers or trimers do exist in the gas phase. As the vapor is compressed along the coexistence line the experimental results indicate an increase in concentration of the molecular species to about 25% at conditions close to the critical point [9]. Resent theoretical considerations of these data reach a similar conclusion [11]. The question to emerge from these findings is, up to what density can the pairing mechanism present in the vapor survive the passage from the dilute vapor to the dense liquid [1,12].Recently, we were able to extend our measurements of the dynamic structure factor S͑Q, v͒ for liquid ru-bidium to densities as low as twice the critical density, where deviations from the metallic behavior are already significant ...

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The Insulator-Metal Transition in Expanded Cesium

Cited by 10 publications

References 11 publications

A modified Van der Waals model for the coexistence curve of expanded metals

A modified Van der Waals model for the coexistence curve of expanded metals

State dependent particle dynamics in liquid alkali metals

Monatomic-Molecular Transition in Expanded Rubidium

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