qha: A Python package for quasiharmonic free energy calculation for multi-configuration systems

Qin, Tian; Zhang, Qi; Wentzcovitch, Renata M.; Umemoto, Koichiro

doi:10.1016/j.cpc.2018.11.003

Cited by 30 publications

(27 citation statements)

References 26 publications

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“…Vibrational density of states (VDOSs) were obtained using a q-point 20×20×20 mesh. The vibrational contribution to the free energy was calculated using the quasiharmonic approximation [27] with the qha code [28].…”

Section: Methodsmentioning

confidence: 99%

Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

Sun,

Zhuang,

Wentzcovitch

2021

Preprint

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We present LDA+Usc calculations of high-spin (HS) and low-spin (LS) states in ferropericlase (fp) with an iron concentration of 18.75%. The Hubbard parameter U is determined self-consistently with structures optimized at arbitrary pressures. We confirm a strong dependence of U on the pressure and spin state. Static calculations confirm that the antiferromagnetic configuration is more stable than the ferromagnetic one in the HS state, consistent with low-temperature measurements. Phonon calculations guarantee the dynamical stability of HS and LS states throughout the pressure range of the Earth mantle. Compression curves for HS and LS states agree well with experiments. Using a non-ideal mixing model for the HS to LS states solid solution, we obtain a crossover starting at ∼45 GPa at room temperature and considerably broader than previous results. The spin-crossover phase diagram is calculated, including vibrational, magnetic, electronic, and non-ideal HS-LS entropic contributions. Our results suggest the mixed-spin state predominates in fp in most of the lower mantle.

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Section: Methodsmentioning

confidence: 99%

Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

Sun,

Zhuang,

Wentzcovitch

2021

Preprint

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“…Multi-configuration QHA (mc-QHA) calculations were performed with the open-source Python code qha [33]. The QHA Helmholtz free energy for each configuration is given by…”

Section: B Thermodynamicsmentioning

confidence: 99%

“…1 suggest the disordered system is indeed possible [29]. We now investigate the thermodynamic properties of HOCδ using the mc-QHA method [33] and the volume dependence of VDoSs of the four supercells. As previously discussed in Sec.…”

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

confidence: 99%

“…Therefore, an ensemble of 1 × 1 × 2 supercell configurations might capture the main effects of disorder in δ. The coexistence of H-bond configurations can be treated with the multiconfiguration quasiharmonic approximation (mc-QHA) [33]. This approach has been used to address the free energy of ice-VII [33] and has successfully described the order-disorder transition in ice-VIII to -VII in a similar H-bond disordering problem [34].…”

Section: Introductionmentioning

confidence: 99%

“…Sec. III presents our computational investigation of the multi-stage process; we address a) energy barriers for proton-hopping, b) vibrational properties and the pressure range of validity of the quasiharmonic approximation (QHA), c) order-disorder transition using mc-QHA [33], its implications for the compressibility, and (001)-projected proton distribution d) neutron diffraction anomalies and disorder, and e) bond-length anomalies and tunneling. Sec.…”

Section: Introductionmentioning

confidence: 99%

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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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Development of a flexible quasi-harmonic-based approach for fast generation of self-consistent thermodynamic properties used in computational thermochemistry

Jofré,

Gheribi,

Harvey

2023

Calphad

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qha: A Python package for quasiharmonic free energy calculation for multi-configuration systems

Cited by 30 publications

References 26 publications

Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

Thermodynamics of spin crossover in ferropericlase: an improved LDA+$U_{sc}$ calculation

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

Development of a flexible quasi-harmonic-based approach for fast generation of self-consistent thermodynamic properties used in computational thermochemistry

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