Anharmonic Nuclear Motion and the Relative Stability of Hexagonal and Cubic ice

Engel, Edgar A.; Monserrat, Bartomeu; Needs, R. J.

doi:10.1103/physrevx.5.021033

Cited by 50 publications

(81 citation statements)

References 63 publications

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“…Nevertheless, a note of caution must be added here. Very recently, Engel, Monserrat, and Needs (2015) have shown in a DFT-based study that anharmonic contributions to the free energy can turn out to be decisive for describing correctly the thermodynamic stability of different ice polymorph with very close quasiharmonic free energies. In particular, it has been shown that anharmonic quantum nuclear effects are decisive in stabilizing the hexagonal I h phase with respect to cubic I c , the latter being a rare form of ice that presents a different stacking of layers of tetrahedrally coordinated water molecules.…”

Section: Molecular Crystalsmentioning

confidence: 99%

“…In the SCP approach, one essentially assumes an harmonic solid with force constants that best represent the real anharmonic crystal, which are determined on the basis of a variational principle. We note that in recent years variants of the SCP approach have been successfully applied to the study of highly anharmonic metallic, molecular, and superconductor materials, in the context of electronic first-principles calculations (Errea, Rousseau, and Bergara, 2011;Errea, Calandra, and Mauri, 2013;Errea, Calandra, and Mauri, 2014;Engel, Monserrat, and Needs, 2015;Errea, et al, 2015).…”

Section: B a Bit Of History And Theorymentioning

confidence: 99%

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Simulation and understanding of atomic and molecular quantum crystals

2017

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Quantum crystals abound in the whole range of solid-state species. Below a certain threshold temperature the physical behavior of rare gases ( 4 He and Ne), molecular solids (H 2 and CH 4 ), and some ionic (LiH), covalent (graphite), and metallic (Li) crystals can be only explained in terms of quantum nuclear effects (QNE). A detailed comprehension of the nature of quantum solids is critical for achieving progress in a number of fundamental and applied scientific fields like, for instance, planetary sciences, hydrogen storage, nuclear energy, quantum computing, and nanoelectronics. This review describes the current physical understanding of quantum crystals formed by atoms and small molecules, as well as the wide palette of simulation techniques that are used to investigate them. Relevant aspects in these materials such as phase transformations, structural properties, elasticity, crystalline defects and the effects of reduced dimensionality, are discussed thoroughly. An introduction to quantum Monte Carlo techniques, which in the present context are the simulation methods of choice, and other quantum simulation approaches (e. g., path-integral molecular dynamics and quantum thermal baths) is provided. The overarching objective of this article is twofold. First, to clarify in which crystals and physical situations the disregard of QNE may incur in important bias and erroneous interpretations. And second, to promote the study and appreciation of QNE, a topic that traditionally has been treated in the context of condensed matter physics, within the broad and interdisciplinary areas of materials science.

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Section: Molecular Crystalsmentioning

confidence: 99%

Section: B a Bit Of History And Theorymentioning

confidence: 99%

Simulation and understanding of atomic and molecular quantum crystals

2017

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“…However, here there is much room for optimism because methods for performing accurate vibrational calculations within DFT are being actively developed. 106,107 We conclude that experiments on hydrogen sulfide vindicate Ashcroft's ideas on superconducting hydrides. It is, however, still unclear whether high-T c superconductivity will be observed in pure hydrogen.…”

Section: A Glimpse Of the Futurementioning

confidence: 99%

Perspective: Role of structure prediction in materials discovery and design

Needs¹,

Pickard

2016

APL Materials

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124

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Materials informatics owes much to bioinformatics and the Materials Genome Initiative has been inspired by the Human Genome Project. But there is more to bioinformatics than genomes, and the same is true for materials informatics. Here we describe the rapidly expanding role of searching for structures of materials using first-principles electronic-structure methods. Structure searching has played an important part in unraveling structures of dense hydrogen and in identifying the record-high-temperature superconducting component in hydrogen sulfide at high pressures. We suggest that first-principles structure searching has already demonstrated its ability to determine structures of a wide range of materials and that it will play a central and increasing part in materials discovery and design.

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“…In this work a vibrational self-consistent field (VSCF) method, described in Ref. 39 and used successfully several times since [40][41][42][43] , is used to include anharmonic effects in our results. This method has been used successfully in high pressure and temperature systems 41,44 , but this study consitutes the first time such a method has been applied to lower mantle materials.…”

Section: B Vibrational Calculationsmentioning

confidence: 99%

First-principles anharmonic vibrational study of the structure of calcium silicate perovskite under lower mantle conditions

Prentice

Needs

2019

Phys. Rev. B

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Calcium silicate perovskite (CaSiO3) is one of the major mineral components of the lower mantle, but has been the subject of relatively little work compared to the more abundant Mg-based materials. One of the major problems related to CaSiO3 that is still the subject of research is its crystal structure under lower mantle conditions -a cubic Pm3m structure is accepted in general, but some have suggested that lower-symmetry structures may be relevant. In this work, we use a fully firstprinciples vibrational self-consistent field (VSCF) method to perform high accuracy anharmonic vibrational calculations on several candidate structures at a variety of points along the geotherm near the base of the lower mantle, in order to investigate the stability of the cubic structure and related distorted structures. Our results show that the cubic structure is the most stable throughout the lower mantle, and that this result is robust against the effects of thermal expansion.

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Anharmonic Nuclear Motion and the Relative Stability of Hexagonal and Cubic ice

Cited by 50 publications

References 63 publications

Simulation and understanding of atomic and molecular quantum crystals

Simulation and understanding of atomic and molecular quantum crystals

Perspective: Role of structure prediction in materials discovery and design

First-principles anharmonic vibrational study of the structure of calcium silicate perovskite under lower mantle conditions

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