Phase Stability and Broken‐Symmetry Transition of Elemental Lithium up to 140 GPa

Rousseau, Roger; Uehara, Kentaro; Klug, D. D.; Tse, John S.

doi:10.1002/cphc.200500117

Cited by 41 publications

(42 citation statements)

References 24 publications

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“…A DFT study by Rousseau et al [8] found a structure of Cmca symmetry to be more stable than I 43d above 88 GPa. This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8]. Cmca-24 consists of threefold coordinated atoms [8].…”

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“…This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8]. Cmca-24 consists of threefold coordinated atoms [8].Ma et al[9] studied high-pressure phases of Li using a combination of ab initio DFT methods and an evolutionary search algorithm, finding a new structure of P4 1 32 symmetry which they calculated to be more stable than Cmca-24 above 300 GPa. This structure contains sixfold coordinated atoms.…”

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confidence: 99%

“…A number of theoretical studies have sought to identify candidate phases at higher pressures [2,8,9]. A DFT study by Rousseau et al…”

mentioning

confidence: 99%

“…This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8]. Cmca-24 consists of threefold coordinated atoms [8].…”

mentioning

confidence: 99%

“…A number of theoretical studies have sought to identify candidate phases at higher pressures [2,8,9]. A DFT study by Rousseau et al [8] found a structure of Cmca symmetry to be more stable than I 43d above 88 GPa. This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8].…”

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Dense Low-Coordination Phases of Lithium

Pickard

Needs²

2009

Phys. Rev. Lett.

108

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Ab initio density-functional-theory calculations and a structure-searching technique are used to identify candidate high-pressure phases of lithium (Li). We predict threefold coordinated structures to be stable in the pressure range 40-450 GPa and fourfold structures at higher pressures. We describe these lowcoordination phases as elemental electrides. All of the stable phases are metallic but the Cmca-24 structure, and two distortions of it which are marginally the most stable in the pressure range 86-106 GPa, are nearly semiconducting with densities of electronic states at the Fermi energy of only a few percent of the free-electron value. DOI: 10.1103/PhysRevLett.102.146401 PACS numbers: 71.15.Nc, 61.66.Àf, 62.50.Àp In the close-packed structures adopted by Li at low pressures [1] the 2s electrons combine to form a half-filled nearly-free-electron band, consistent with the picture of a simple alkali metal. However, strong deviations from the canonical picture develop at higher pressures. Overlap of the Li 1s core electrons on neighboring atoms under strong compression has a profound effect upon the structures, which adopt lower coordination structures [2,3].The close-packed face-centered-cubic (fcc) phase of Li transforms to a structure of I 43d space group symmetry [4] at $40 GPa, via an intermediate phase of R 3m symmetry [3]. The R 3m phase has a distorted fcc structure, but the I 43d structure departs very substantially from close packing. I 43d has three short interatomic distances giving threefold coordination. Calculations show that the valence electronic density of states (e-DOS) dips around the Fermi energy (E F ) [3]. These features are consistent with the picture that reduced coordination numbers at high pressures arise from a Jahn-Teller-like distortion [2]. Calculations of the high-pressure phases also show an accumulation of electronic charge density within the interstitial region as the 2s electron density is pushed away from the atomic cores by Coulomb repulsion, Pauli exclusion, and the orthogonality of core and valence orbitals [2,3,5].Experiments suggest another phase transition at 60-70 GPa, although the new structure has not been determined [6,7]. A number of theoretical studies have sought to identify candidate phases at higher pressures [2,8,9]. A DFT study by Rousseau et al.[8] found a structure of Cmca symmetry to be more stable than I 43d above 88 GPa. This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8]. Cmca-24 consists of threefold coordinated atoms [8].Ma et al.[9] studied high-pressure phases of Li using a combination of ab initio DFT methods and an evolutionary search algorithm, finding a new structure of P4 1 32 symmetry which they calculated to be more stable than Cmca-24 above 300 GPa. This structure contains sixfold coordinated atoms. On the other hand, recent hightemperature DFT molecular dynamics simulations found fourfold coordinated Li atoms in the pressure range 150-810 GPa [10].Superconductivity has been observed in Li up...

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confidence: 99%

“…A number of theoretical studies have sought to identify candidate phases at higher pressures [2,8,9]. A DFT study by Rousseau et al…”

mentioning

confidence: 99%

“…This structure is named Cmca-24, appending the number of atoms in the conventional unit cell [8]. Cmca-24 consists of threefold coordinated atoms [8].…”

mentioning

confidence: 99%

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confidence: 99%

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