cij: A Python code for quasiharmonic thermoelasticity

Luo, Chenxing; Deng, Xin; Wang, Wenzhong; Shukla, Gaurav; Wu, Zhongqing; Wentzcovitch, Renata M.

doi:10.1016/j.cpc.2021.108067

Cited by 18 publications

(11 citation statements)

References 62 publications

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“…The HS to LS state change in iron in these systems occurs only on the A‐site of Pv and PPv at pressures considerably lower than the Pv to PPv transition (Hsu et al., 2011; Y. Yu et al., 2012) and is not expected to affect the current results significantly. Thermodynamic and thermoelastic properties are here recalculated using the quasi‐harmonic approximation (Wallace, 1972) using the qha (Qin et al., 2019) and cij codes (Luo et al., 2021). The performance of these approaches for thermodynamic and thermoelastic properties have been extensively documented (Wentzcovitch, Wu, & Carrier, 2010; Wentzcovitch, Yu, & Wu, 2010).…”

Section: Methods and Calculation Detailsmentioning

confidence: 99%

The Post‐Perovskite Transition in Fe‐ and Al‐Bearing Bridgmanite: Effects on Seismic Observables

et al. 2023

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The primary phase of the Earth’s lower mantle, (Al, Fe)‐bearing bridgmanite, transitions to the post‐perovskite (PPv) phase at Earth’s deep mantle conditions. Despite extensive experimental and ab initio investigations, there are still important aspects of this transformation that need clarification. Here, we address this transition in (Al3+, Fe3+)‐, (Al3+)‐, (Fe2+)‐, and (Fe3+)‐bearing bridgmanite using ab initio calculations and validate our results against experiments on similar compositions. Consistent with experiments, our results show that the onset transition pressure and the width of the two‐phase region depend distinctly on the chemical composition: (a) Fe3+‐, Al3+‐, or (Al3+, Fe3+)‐alloying increases the transition pressure, while Fe2+‐alloying has the opposite effect; (b) in the absence of coexisting phases, the pressure‐depth range of the Pv‐PPv transition is likely too broad to cause a sharp D” discontinuity (<30 km); (c) the average Clapeyron slope of the two‐phase regions are consistent with previous measurements, calculations in MgSiO3, and inferences from seismic data. In addition, (d) we observe a softening of the bulk modulus in the two‐phase region. The consistency between our results and experiments gives us the confidence to proceed and examine this transition in aggregates with different compositions computationally, which will be fundamental for resolving the most likely chemical composition of the D" region by analyses of tomographic images.

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Section: Methods and Calculation Detailsmentioning

confidence: 99%

The Post‐Perovskite Transition in Fe‐ and Al‐Bearing Bridgmanite: Effects on Seismic Observables

et al. 2023

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“…To get the full elastic constant tensor, the vibrational density of states (VDoSs) and free energy of several strained configurations are needed in the conventional methods. Instead, the method used in this study (Luo et al., 2021; Wu & Wentzcovitch, 2011; Zou et al., 2018) only requires knowledge of the volume dependence of vibrational properties under hydrostatic pressure, avoiding the VDoSs calculations for the configurations under strains. This method involves a moderate computational workload, no more than 10% of those of conventional ones.…”

Section: Methodsmentioning

confidence: 99%

“…Calculations in this study were performed with the Quantum ESPRESSO package (Giannozzi et al., 2009) based on the DFT and the cij package (Luo et al., 2021). Both the local density approximation (LDA) (Kohn & Sham, 1965; Perdew & Zunger, 1981) and generalized gradient approximation (GGA) (Perdew et al., 1996) were adopted as the exchange‐correlation functional except density‐functional‐perturbation‐theory (DFPT) calculations for VDoSs, where only LDA was used.…”

Section: Methodsmentioning

confidence: 99%

Elastic Anisotropy of Lizardite at Subduction Zone Conditions

Deng

Luo

et al. 2022

Geophysical Research Letters

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Subduction zones transport water into Earth's deep interior through slab subduction. Serpentine minerals, the primary hydration product of ultramafic peridotite, are abundant in most subduction zones. Characterization of their high‐temperature elasticity, particularly their anisotropy, will help us better estimate the extent of mantle serpentinization and the Earth's deep water cycle. Lizardite, the low‐temperature polymorph of serpentine, is stable under the P‐T conditions of cold subduction slabs (<260°C at 2 GPa), and its high‐temperature elasticity remains unknown. Here we report ab initio elasticity and acoustic wave velocities of lizardite at P‐T conditions of subduction zones. Our static results agree with previous studies. Its high‐temperature velocities are much higher than previous experimental‐based lizardite estimates with chrysotile but closer to antigorite velocities. The elastic anisotropy of lizardite is much larger than that of antigorite and could better account for the observed large shear‐wave splitting in some cold slabs such as Tonga.

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“…Phonon frequency continuity between adjacent volume points is established using eigenvectors similarity described in Ref. [50].…”

Section: B Pressure Dependence Of Vdos Proton Stability and Tunneling...mentioning

confidence: 99%

Ab initio investigation of H-bond disordering in $δ$-AlOOH

Luo,

Umemoto,

Wentzcovitch

2021

Preprint

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δ-AlOOH (δ) is a high-pressure hydrous phase that participates in the deep geological water cycle. At 0 GPa, δ has asymmetric hydrogen bonds (H-bonds). Under pressure, it exhibits H-bond disordering, tunneling, and finally, H-bond symmetrization at ∼18 GPa. This study investigates these 300 K pressure-induced state changes in δ with ab initio calculations. H-bond disordering in δ was modeled using supercell multi-configuration quasiharmonic calculations. We examine: (a) energy barriers for proton jumps, (b) the pressure dependence of phonon frequencies, (c) 300 K compressibility, (d) neutron diffraction pattern anomalies, and (e) compare ab initio bond lengths with measured ones. Such thorough and systematic comparisons indicate that: (a) proton "disorder" has a restricted meaning when applied to δ. Nevertheless, H-bonds are disordered between 0 and 8 GPa, and a gradual change in H-bond configuration results in enhanced compressibility. (b) several structural and vibrational anomalies at 8 GPa are consistent with the disappearance of a particular (HOC-12) H-bond configuration and its change into another one (HOC-11*). (c) between 8-11 GPa, H-bond configuration (HOC-11*) is generally ordered, at least in short-to mid-range scale. (d) between 11.5-18 GPa, H-bond lengths approach a critical value that impedes compression, resulting in decreased compressibility. In this pressure range, especially approaching H-bond symmetrization at ∼18 GPa, anharmonicity and tunneling should play an essential role in the proton dynamics. Further simulations accounting for these effects are desirable to clarify the protons' state in this pressure range.

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cij: A Python code for quasiharmonic thermoelasticity

Cited by 18 publications

References 62 publications

The Post‐Perovskite Transition in Fe‐ and Al‐Bearing Bridgmanite: Effects on Seismic Observables

The Post‐Perovskite Transition in Fe‐ and Al‐Bearing Bridgmanite: Effects on Seismic Observables

Elastic Anisotropy of Lizardite at Subduction Zone Conditions

Ab initio investigation of H-bond disordering in $δ$-AlOOH

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