Molecular dynamics simulation of phase competition in terbium

Song, Hantao; Mendelev, Mikhail I.

doi:10.1063/1.5054008

Cited by 7 publications

(3 citation statements)

References 41 publications

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“…Interestingly, a similar crystallization mechanism was observed for pure Tb in Ref. 32. We also note that the fraction of the Z16 which is typical for the Laves phases is slightly higher in the liquid Cu 64.5 Zr 35.5 alloy described by the FS2 potential than that in the same liquid alloy described by the FS1 potential.…”

Section: Molecular Dynamics Simulation Of Solidification In Cu-zr Alloyssupporting

confidence: 85%

Development of a semi-empirical potential suitable for molecular dynamics simulation of vitrification in Cu-Zr alloys

Mendelev

Sun

Zhang

et al. 2019

The Journal of Chemical Physics

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The fast increase in available computation power allowed us to decrease the cooling rate in molecular dynamics (MD) simulation of vitrification by several orders of magnitude. While the reliability of the MD simulation should obviously benefit from this increase in the computational power, in some cases, it led to unexpected results. In particular, Ryltsev et al. [J. Chem. Phys. 149, 164502 (2018)] found that the most popular potentials for the Cu-Zr and Cu-Zr-Al alloys from Mendelev et al. [Philos. Mag. 89, 967 (2009)] and Cheng et al. [Phys. Rev. Lett. 102, 245501 (2009)] do not actually describe good glass forming systems but in contradiction with experiment predict rather fast crystallization of the Cu 64.5 Zr 35.5 alloy which is the well-known example of bulk metallic glasses. In this paper, we present a new Cu-Zr semiempirical potential suitable to simulate vitrification. No crystal nucleation was observed in MD simulation using this potential in the concentration range from 75% to 5% of Zr. Since the new potential leads to about the same liquid structure and viscosity as the Cu-Zr potential from Mendelev et al. [Philos. Mag. 89, 967 (2009)] which failed to describe the good glass formability, our study clearly shows that no reliable conclusions about the glass formability can be deduced based solely on the analysis of the liquid properties and a nucleation/crystal growth study should be performed to address this question.

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Section: Molecular Dynamics Simulation Of Solidification In Cu-zr Alloyssupporting

confidence: 85%

Development of a semi-empirical potential suitable for molecular dynamics simulation of vitrification in Cu-Zr alloys

Mendelev

Sun

Zhang

et al. 2019

The Journal of Chemical Physics

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“…Therefore, instead of the single-pathway scenario, we can consider a complex process in which nucleation is facilitated by forming an intermediate phase with a high-nucleation rate. For example, it has been observed that the bcc phase can nucleate before the face-centered, cubic (fcc) or hcp phases in a few alloys in which the fcc/hcp phase is the most stable one ( 20 – 24 ). Could the bcc phase also facilitate hcp iron nucleation and relate to the inner core nucleation paradox?…”

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confidence: 99%

Two-step nucleation of the Earth’s inner core

Sun

Zhang

Mendelev

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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The Earth's inner core started forming when molten iron cooled below the melting point. However, the nucleation mechanism, which is a necessary step of crystallization, has not been well understood. Recent studies have found that it requires an unrealistic degree of undercooling to nucleate the stable, hexagonal, close-packed (hcp) phase of iron that is unlikely to be reached under core conditions and age. This contradiction is referred to as the inner core nucleation paradox. Using a persistent embryo method and molecular dynamics simulations, we demonstrate that the metastable, body-centered, cubic (bcc) phase of iron has a much higher nucleation rate than does the hcp phase under inner core conditions. Thus, the bcc nucleation is likely to be the first step of inner core formation, instead of direct nucleation of the hcp phase. This mechanism reduces the required undercooling of iron nucleation, which provides a key factor in solving the inner core nucleation paradox. The two-step nucleation scenario of the inner core also opens an avenue for understanding the structure and anisotropy of the present inner core.

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“…Instead of the scenario described above, where the melt in the Earth's core crystallized directly into the hcp phase, we can consider a complex process where nucleation is facilitated by forming a metastable phase with a high nucleation rate [17,18]. For example, it has been observed that the bcc phase can nucleate before facecentered cubic (fcc) or hcp phases in a few alloys where the fcc/hcp phase is the most stable one [19][20][21][22][23]. Could the bcc phase also facilitate hcp iron nucleation and relate to the inner core nucleation paradox?…”

mentioning

confidence: 99%

Two-step nucleation of the Earth's inner core

Sun,

Zhang,

Mendelev

et al. 2021

Preprint

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It has long been assumed the Earth's solid inner core started to grow when molten iron cooled to its melting point. However, the nucleation mechanism, which is a necessary step of crystallization, has not been well understood. Recent studies found it requires an unrealistic degree of undercooling to nucleate the stable hexagonal closepacked (hcp) phase of iron, which can never be reached under the actual Earth's core conditions. This contradiction leads to the inner core nucleation paradox [1]. Here, using a persistent-embryo method and molecular dynamics simulations, we demonstrate that the metastable body-centered cubic (bcc) phase of iron has a much higher nucleation rate than the hcp phase under inner-core conditions. Thus, the bcc nucleation is likely to be the first step of inner core formation instead of direct nucleation of the hcp phase. This mechanism reduces the required undercooling of iron nucleation, which provides a key factor to solve the inner-core nucleation paradox. The two-step nucleation scenario of the inner core also opens a new avenue for understanding the structure and anisotropy of the present inner core.

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Molecular dynamics simulation of phase competition in terbium

Cited by 7 publications

References 41 publications

Development of a semi-empirical potential suitable for molecular dynamics simulation of vitrification in Cu-Zr alloys

Development of a semi-empirical potential suitable for molecular dynamics simulation of vitrification in Cu-Zr alloys

Two-step nucleation of the Earth’s inner core

Two-step nucleation of the Earth's inner core

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