Effect of octupole–octupole interactions on the thermodynamic stability of the low-pressure crystalline state of SnI4 molecular crystals

Fuchizaki, Kazuhiro; Nagai, K.

doi:10.1016/j.ssc.2004.08.003

Cited by 6 publications

(3 citation statements)

References 7 publications

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“…The production of the amorphous phase from two different crystal structures seems to undermine the pseudomelting hypothesis as suggested by Fuchizaki et al 20 The two materials that have been cited as examples of pseudomelting are water-ice 9 and quartz, 21 and both are thought to have the negative dT m / dP melting slopes necessary for the melt curve to return to low temperature: a requirement for explaining room-temperature amorphization according to this model. That the melting slope of SnI 4 is positive, according to molecular-dynamics simulations 15,20,22,23 and direct measurement, 23 seems to eliminate this hypothesis. Moreover, pseudomelting may not explain high-pressure amorphization, in general, as many systems produce an amorphous state appearing like a highly disordered crystal 24 or exhibiting a memory of the crystal phase from which it came.…”

Section: Discussionmentioning

confidence: 99%

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

2010

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We have measured the pressure-induced amorphization of tin iodide ͑SnI 4 ͒ as a function of temperature and found a small ͑Ͻ1 GPa͒ increase in the initiation pressure of the transition from 293 to 523 K. We have also determined the P-V equation of state while the material undergoes the amorphization, including multiple compressions of a single sample, using a diamond-anvil cell and x-ray diffraction. Apparent stiffening upon multiple compression of the sample can be explained by either an increase in nonhydrostaticity during loading or, possibly, changes in the initial crystal structure upon decompression recrystallization. Contrary to previous interpretations of the amorphization being a two-stage process, with SnI 4 converting to a second ͑unidentified͒ crystalline phase before the loss of Bragg intensities, the present experiments show that it is also possible to amorphize SnI 4 without the appearance of the second crystalline phase. While the new diffraction peaks appear upon the first compression of a sample, subsequent compressions of the same sample do not show these new peaks; instead, long-range ordering of the original cubic crystal structure is lost.

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Section: Discussionmentioning

confidence: 99%

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

2010

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“…4) The octupole-octupole interaction between the molecules was not sufficient for the compensation. 4) An ISM of the TIP4P type mentioned in the Introduction is definitely easier to take the effects of the charge distribution into consideration than taking successive contributions of the multipole expansion into the interaction.…”

Section: Numerical Calculationmentioning

confidence: 99%

“…However, only some leading contributions in the expansion can be considered in practice, and their implementation in actual numerical calculations is by no means an easy task. 4) When applying multipole expansions, charges are not necessarily constrained on a molecule. Indeed, the fast multipole method (FMM) for evaluating Coulomb potentials between spatially distributed charges was extensively discussed by Greengard.…”

Section: Introductionmentioning

confidence: 99%

Application of the Generalized Ewald Method to a Molecular System

Fuchizaki

2010

J. Phys. Soc. Jpn.

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A classical interaction site model is still of great value for a complex substance to which firstprinciples calculations are not easily applied. In simulations using the interaction site model, a tail of potential other than the Coulomb potential is usually ignored. However, such a cutoff of potential may not be justifiable under some thermodynamic conditions, or in circumstances where precise structural and/or thermodynamic properties have to be investigated. Here, we consider a molecular system in which a molecule or an atomic cluster contains several interaction sites. These interaction sites are connected via inverse power interactions. By attaching a virtual charge to an interaction site, all inverse power interactions, including the Coulomb interactions between true electric charges, are formally treated in a unified fashion. The periodicity introduced by the periodic boundary condition, employed in simulations to eliminate the effects of surfaces, then allows us to adopt the idea of an Ewald sum, thereby being free from the cutoff. The Ewald sum is taken for the sum of the interactions, making use of the formula for the generalized zeta function proposed by the author. As an example, the potential energy of a molecular crystal, SnI 4 , in the low-pressure crystalline state, and of solid argon is examined, where van der Waals interactions bring about cohesion in these crystals. The Lennard-Jones potential is employed to model the cohesive interaction. The treatment is extended to molecular dynamics as well. The equations of motion that can generate an isobaric ensemble are derived. The technical aspects when carrying out large-scale simulations utilizing the Ewald method are briefly mentioned.

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Polyamorphism in tin tetraiodide

Fuchizaki

Hase

Yamada

et al. 2009

The Journal of Chemical Physics

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The discovery of a first-order phase transition in fluid phosphorus aroused renewed interest in polyamorphism in liquids with a locally tetrahedral molecular structure. We have performed in situ synchrotron x-ray diffraction measurements on tin tetraiodide, which consists of SnI4 tetrahedral molecules at ambient pressure, and established that the liquid forms existing above and below 1.5 GPa, where the slope of the melting curve of the solid phase changes abruptly, have different structures. This discovery offers evidence of thermodynamically stable polyamorphism in general compounds as well as in elements. A possible phase diagram that includes the two amorphous states already found is proposed based on the pseudobinary regular solution model. The vertex-to-face orientation between the nearest molecules plays a key role in the transition from the low-pressure to the high-pressure liquid phase.

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Effect of octupole–octupole interactions on the thermodynamic stability of the low-pressure crystalline state of SnI4 molecular crystals

Cited by 6 publications

References 7 publications

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

Equation of state, phase stability, and amorphization ofSnI4at high pressure and temperature

Application of the Generalized Ewald Method to a Molecular System

Polyamorphism in tin tetraiodide

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