Controlling the Bonding and Band Gaps of Solid Carbon Monoxide with Pressure

Sun, Junqiang; Klug, D. D.; Pickard, Chris J.; Needs, R. J.

doi:10.1103/physrevlett.106.145502

Cited by 65 publications

(95 citation statements)

References 31 publications

(56 reference statements)

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“…AIRSS has been successfully employed in finding low-energy structures in many systems, including group 14 elements and their compounds. [39][40][41][42][43][44] We performed searches for structures with up to 24 atoms per unit cell.…”

Section: Ab Initio Calculations and Structure Searchingmentioning

confidence: 99%

Low-energy tetrahedral polymorphs of carbon, silicon, and germanium

Mújica

Pickard

Needs³

2015

Phys. Rev. B

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Searches for low-energy tetrahedral polymorphs of carbon and silicon have been performed using density functional theory computations and the ab initio random structure searching (AIRSS) approach. Several of the hypothetical phases obtained in our searches have enthalpies that are lower or comparable to those of other polymorphs of group 14 elements that have either been experimentally synthesized or recently proposed as the structure of unknown phases obtained in experiments, and should thus be considered as particularly interesting candidates. A structure of P bam symmetry with 24 atoms in the unit cell was found to be a low energy, low-density metastable polymorph in carbon, silicon, and germanium. In silicon, Pbam is found to have a direct band gap at the zone center with an estimated value of 1.4 eV, which suggests applications as a photovoltaic material. We have also found a low-energy chiral framework structure of P 41212 symmetry with 20 atoms per cell containing fivefold spirals of atoms, whose projected topology is that of the so-called Cairo-type twodimensional pentagonal tiling. We suggest that P41212 is a likely candidate for the structure of the unknown phase XIII of silicon. We discuss Pbam and P41212 in detail, contrasting their energetics and structures with those of other group 14 elements, particularly the recently proposed P42/ncm structure, for which we also provide a detailed interpretation as a network of tilted diamond-like tetrahedra.

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Section: Ab Initio Calculations and Structure Searchingmentioning

confidence: 99%

Low-energy tetrahedral polymorphs of carbon, silicon, and germanium

Mújica

Pickard

Needs³

2015

Phys. Rev. B

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“…More precise methods than DFT might be required to clarify the structural sequence as the enthalpy differences are so small. Although the O=O bond in the O 2 molecule is not as strong as the N≡N and C≡O triple bonds, O 2 polymerizes at a much higher pressure than N 2 (∼110 GPa [15]) and CO (experiments show that CO polymerizes at about 5 GPa [18] while calculations predict that it could even polymerize at ambient pressure [19]). The fact that the molecular phases persist to pressures as high as 1.9 TPa is intriguing.…”

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confidence: 99%

Persistence and Eventual Demise of Oxygen Molecules at Terapascal Pressures

et al. 2012

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Computational searches for structures of solid oxygen under pressures in the multi TPa range have been carried out using density-functional-theory methods. We find that molecular oxygen persists to about 1.9 TPa at which it transforms into a semiconducting square spiral-like polymeric structure (I41/acd) with a band gap of ∼3.0 eV. Solid oxygen forms a metallic zig-zag chain-like structure (Cmcm) at about 3.0 TPa, but the chains in each layer gradually merge as the pressure is increased and a structure of F mmm symmetry forms at about 9.5 TPa in which each atom has four nearest neighbors. The superconducting properties of molecular oxygen do not vary much with compression, although the structure becomes more symmetric. The electronic properties of oxygen have a complex evolution with pressure, swapping between insulating, semiconducting and metallic. Among the simple molecules studied at high pressures, oxygen has attracted particular attention due to its fundamental importance and intriguing properties. [1][2][3][4][5] For example, oxygen is the only known elemental molecule that exhibits magnetism, which adds substantial complexity to its phase diagram. When liquid oxygen is cooled at ambient pressure it undergoes a sequence of transitions to the γ, β and α solid phases at 54.39, 43.76 and 23.88 K, respectively [6]. Upon increase of pressure the monoclinic α-O 2 (C2/m) phase transforms into an orthorhombic δ-O 2 (F mmm) phase at about 3 GPa and to -O 2 at about 10 GPa. The structure of -O 2 has only recently been solved by x-ray diffraction (XRD) studies of single crystal [3] and powder [4] samples, although its vibrational spectrum was reported more than 20 years earlier [7]. The unit cell of -O 2 has C2/m symmetry and contains four O 2 molecules forming O 8 units. Both α and δ-O 2 are antiferromagnetic and the magnetic collapse at the δ-transition was predicted using molecular dynamics simulations [8]. This breakdown of the long-range antiferromagnetic order at about 8 GPa was recently observed in a neutron scattering experiment [2]. Density functional theory (DFT) studies have found another chain-like structure to be energetically slightly more favorable than the O 8 structure [9,10], although it has not been observed in experiments.Recent experiments [5] have shown that insulating -O 2 remains stable up to about 96 GPa before undergoing a continuous displacive and isosymmetric transition to the ζ phase, in agreement with earlier predictions [10]. The metallic ζ phase [11,12] has C2/m symmetry [2] and superconducts at temperatures below 0.6 K [1]. Manybody perturbation theory GW calculations [13,14] have suggested that the metal-insulator transition occurs at lower pressures than the measured -ζ transition pressure of 96 GPa. The above information, however, covers only a small part of the phase diagram and rather little is known about pure oxygen at pressures above 100 GPa.A previous DFT study reported that oxygen molecules persist to at least 250 GPa [10]. It is interesting to speculate about the highest p...

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“…However, several recent theoretical calculations have predicted the stabilization of 2D layer structures at very high presssures. Those predictions include 2D polymeric-CO in Cmcm [10], partially ionized extended layers of H 2 O in P2 1 [11], and the graphene-like structure suggested for recently discovered H 2 -IV [12]. In this regard, the cg-to LP-N transition is not surprising, but provides significant implications to those transitions in other molecular systems and, together, the pressure-induced chemistry in dense solids.…”

Section: Phase Diagram Of Nitrogenmentioning

confidence: 79%

“…In fact, recent theoretical calculations have shown that many, if not all, molecular solids transform into extended solids with more itinerant electrons in covalent or metallic network structures. Figure 3 summarizes a selected set of extended structures previously predicted in terms of first principles density functional theories [10][11][12][13][14][15]. Note that not all of these structures have been found experimentally except a few --the 3D I2 1 3 (cg-N), 2D Pba2 (LP-N), and 0D-C2/m (ε-O 2 or a cluster of (O 2 ) 4 [16].…”

Section: Chemistry In Dense Solidsmentioning

confidence: 99%

High energy density nitrogen-rich extended solids

Yoo¹,

Tomasino²,

Smith³

et al. 2017

AIP Conference Proceedings

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Abstract.Many simple molecules such as N 2 and CO 2 have the potential to form extended "polymeric" solids under extreme conditions, which can store a large sum of chemical energy in its three-dimensional network structures made of strong covalent bonds. Diatomic nitrogen is particularly of interest because of the uniquely large energy difference between the single (160 kJ/mol) and triple (950 kJ/mol) bonds. As such, the transformation of singly bonded polymeric nitrogen back to triply bonded diatomic nitrogen molecules can release large energy (~33 kJ/cm 3 -three times that of HMX) without any negative environmental impact. Therefore, the goal of the present study has been to investigate the transformation of nitrogen and nitrogen-rich compounds to new singly bonded nitrogen-rich solids at high pressures and temperatures, using heated diamond anvil cells, Raman spectroscopy, and third-generation synchrotron x-ray diffraction. Recently, we have found a new form of singly bonded layered polymeric nitrogen (LP-N), synthesized in the stability pressure-temperature field higher than that of cg-N. This new phase is characterized by a 2D layered structure similar to the predicted Pba2 and two colossal Raman bands, arising from two groups of highly polarized nitrogen atoms. This result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry lowering 3D cgto 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N. In this paper, we will review this finding of LP-N, update the phase diagram of nitrogen, and offer a chemistry view of pressure-induced transformations in dense molecular solids.

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Controlling the Bonding and Band Gaps of Solid Carbon Monoxide with Pressure

Cited by 65 publications

References 31 publications

Low-energy tetrahedral polymorphs of carbon, silicon, and germanium

Low-energy tetrahedral polymorphs of carbon, silicon, and germanium

Persistence and Eventual Demise of Oxygen Molecules at Terapascal Pressures

High energy density nitrogen-rich extended solids

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