Electronic and structural properties of dense liquid and amorphous nitrogen

Boates, Brian; Bonev, Stanimir

doi:10.1103/physrevb.83.174114

Cited by 34 publications

(29 citation statements)

References 43 publications

(50 reference statements)

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“…The liquid character shifts continuously with pressure from 3-to 4-coordination before freezing into tetrahedral-like amorphous solids, consistent with the local structure of the proposed underlying crystalline phases (3,6,22,23). The mixture of 3-and 4-coordinated carbon in the new liquid phase bears analogy to the low-T amorphous solid (5, 7); a similar analogy also exists between polymeric liquid and low-T amorphous nitrogen (24). Fig.…”

Section: Resultssupporting

confidence: 75%

Stability of dense liquid carbon dioxide

Boates

Teweldeberhan

Bonev

2012

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

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We present ab initio calculations of the phase diagram of liquid CO 2 and its melting curve over a wide range of pressure and temperature conditions, including those relevant to the Earth. Several distinct liquid phases are predicted up to 200 GPa and 10,000 K based on their structural and electronic characteristics. We provide evidence for a first-order liquid-liquid phase transition with a critical point near 48 GPa and 3,200 K that intersects the mantle geotherm; a liquid-liquid-solid triple point is predicted near 45 GPa and 1,850 K. Unlike known first-order transitions between thermodynamically stable liquids, the coexistence of molecular and polymeric CO 2 phases predicted here is not accompanied by metallization. The absence of an electrical anomaly would be unique among known liquid-liquid transitions. Furthermore, the previously suggested phase separation of CO 2 into its constituent elements at lower mantle conditions is examined by evaluating their Gibbs free energies. We find that liquid CO 2 does not decompose into carbon and oxygen up to at least 200 GPa and 10,000 K.high pressure | density functional theory | first principles molecular dynamics | polymerization A t ambient conditions, the sp-valent second-row elements C, N, and O form simple volatile molecules characterized by double and triple bonds. These materials often undergo dramatic transformations at high pressures into extended single-bonded covalent phases with novel optical, energetic, and mechanical properties (1, 2). The polymerization of solid carbon dioxide has been studied extensively as a prototype for the evolution of a chemical bond under compression (2-7). CO 2 also plays a fundamental role in the physics and chemistry of the Earth interior and its climate (8)(9)(10)(11)(12)(13)(14). However, the thermodynamic, chemical, and physical properties of CO 2 at the high temperature (above 2,000 K) and pressure conditions relevant to planetary interiors remain largely unknown.A critical factor for the Earth's climate is the concentration of CO 2 in the atmosphere, which is controlled by a complicated dynamical cycle involving terrestrial reservoirs and fluxes (8). The vast majority of CO 2 is stored in the mantle primarily in the form of Ca and Mg carbonates (8-13). Experimental (11) and theoretical (13) works suggest that CO 2 is produced at high pressure (P) and temperature (T) during decarbonating reactions with silica in subducted basalts and is subsequently released into the ocean and atmosphere during volcanic activity (8). Moreover, reactions between silica and free CO 2 may also take place under such conditions, leading to the formation of silicon carbonates (15). Whether free CO 2 is stable or decomposes into oxygen and diamond in the mantle is currently unclear (11,12,16,17). Therefore, understanding the stability of CO 2 is a major challenge in establishing the more general issue of terrestrial cycles of C and CO 2 . Furthermore, the presence of CO 2 fluid is believed to be responsible for partial melting and rheological we...

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Section: Resultssupporting

confidence: 75%

Stability of dense liquid carbon dioxide

Boates

Teweldeberhan

Bonev

2012

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

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“…The structure of this phase was found to be orthorhombic P nma -for atomic positions and physical properties see Table I. The semimetallic character of the trans-cis phase is consistent with observations in liquid nitrogen, where it was found that conductivity of liquid-N is strongly correlated with the amount of 2c-N atoms representing insides of chain molecules 64 . The only previously studied phase made up of infinite trans-cis chains is orthorhombic ch-phase, which was, however, found to be both mechanically (Born criteria violation) and dynamically (imaginary phonon modes) unstable up to the investigated 360 GPa 51 .…”

Section: E Trans-cis Chain Phasesupporting

confidence: 82%

Transformation pathways in high-pressure solid nitrogen: From molecular N2 to polymeric cg-N

Plašienka

Martoňák

2015

The Journal of Chemical Physics

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The transformation pathway in high-pressure solid nitrogen from N 2 molecular state to polymeric cg-N phase was investigated by means of ab initio molecular dynamics and metadynamics simulations. In our study, we observed a transformation mechanism starting from molecular Immm phase that initiated with formation of trans-cis chains. These chains further connected within layers and formed a chain-planar state, which we describe as a mixture of two crystalline structures -trans-cis chain phase and planar phase, both with P nma symmetry. This mixed state appeared in molecular dynamics performed at 120 GPa and 1500 K and in the metadynamics run at 110 GPa and 1500 K, where the chains continued to reorganize further and eventually formed cg-N. During separate simulations, we also found two new phases -molecular P 2 1 /c and two-threecoordinated chain-like Cm. The transformation mechanism heading towards cg-N can be characterized as a progressive polymerization process passing through several intermediate states of variously connected transcis chains. In the final stage of the transformation chains in the layered form rearrange collectively and develop new intraplanar as well as interplanar bonds leading to the geometry of cg-N. Chains with alternating trans and cis conformation were found to be the key entity -structural pattern governing the dynamics of the simulated molecular-polymeric transformation in compressed nitrogen.

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“…Most importantly, we have compared the PBE and HSE06-optimized structure and found no evidence of a Peierls distortion ensuing after optimization of the PBE structures conducted with HSE06, in contrast to what was found for a polymeric phase of nitrogen39. We attribute it to the fact that the studied structures contain isolated ions or molecules, and do not exhibit extended motifs (chains, layers) for which one can expect a Peierls distortion.…”

Section: Resultsmentioning

confidence: 70%

Hexacoordinated nitrogen(V) stabilized by high pressure

Kurzydłowski

Zaleski‐Ejgierd

2016

Sci Rep

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In all of its known connections nitrogen retains a valence shell electron count of eight therefore satisfying the golden rule of chemistry - the octet rule. Despite the diversity of nitrogen chemistry (with oxidation states ranging from + 5 to −3), and despite numerous efforts, compounds containing nitrogen with a higher electron count (hypervalent nitrogen) remain elusive and are yet to be synthesized. One possible route leading to nitrogen’s hypervalency is the formation of a chemical moiety containing pentavalent nitrogen atoms coordinated by more than four substituents. Here, we present theoretical evidence that a salt containing hexacoordinated nitrogen(V), in the form of an NF6− anion, could be synthesized at a modest pressure of 40 GPa (=400 kbar) via spontaneous oxidation of NF3 by F2. Our results indicate that the synthesis of a new class of compounds containing hypervalent nitrogen is within reach of current high-pressure experimental techniques.

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Electronic and structural properties of dense liquid and amorphous nitrogen

Cited by 34 publications

References 43 publications

Stability of dense liquid carbon dioxide

Stability of dense liquid carbon dioxide

Transformation pathways in high-pressure solid nitrogen: From molecular N2 to polymeric cg-N

Hexacoordinated nitrogen(V) stabilized by high pressure

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