The generalized quasiharmonic approximation via space group irreducible derivatives

Mathis, Mark A.; Khanolkar, Amey; Fu, Lyuwen; Bryan, Matthew S.; Dennett, Cody A.; Rickert, Karl; Mann, J. Matthew; Winn, Barry; Abernathy, Douglas L.; Manley, Michael E.; Hurley, David H.; Marianetti, Chris A.

doi:10.48550/arxiv.2202.14016

Cited by 2 publications

(4 citation statements)

References 74 publications

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“…It should be noted that all irreducible derivatives within 2 ŜC , which has a multiplicity of 32, can be extracted from supercells with multiplicities of 4 (i.e., 12 atoms per supercell). The Born effective charges (Z ⋆ U = 5.54 and Z ⋆ O = −2.77) of the U and O ions and the dielectric constant (ǫ = 5.69) were used to account for LO-TO splitting [50,51].…”

Section: Computational Detailsmentioning

confidence: 99%

Capturing the ground state of uranium dioxide from first principles: crystal distortion, magnetic structure, and phonons

Zhou¹,

Ma²,

Xiao³

et al. 2022

Preprint

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Uranium dioxide (UO2) remains a formidable challenge for first-principles approaches due to the complex interplay among spin-orbit coupling, Mott physics, magnetic ordering, and crystal distortions. Here we use DFT+U to explore UO2 at zero temperature, incorporating all the aforementioned phenomena. The technical challenge is to navigate the many metastable electronic states produced by DFT+U , which is acomplished using f -orbital occupation matrix control to search for the ground state. We restrict our search to the high-symmetry ferromagnetic phase, including spin-orbit coupling, which produces a previously unreported occupation matrix. This newfound occupation matrix is then used as an initialization to explore the broken symmetry phases. We find the oxygen cage distortion of the 3k antiferromagnetic state to be in excellent agreement with experiments, and both the spin-orbit coupling and the Hubbard U are critical ingredients. We demonstrate that only select phonon modes have a strong dependence on the Hubbard U , whereas magnetic ordering has only a small influence overall. We perform measurements of the phonon dispersion curves using inelastic neutron scattering, and our calculations show good agreement when using reasonable values of U . The quantitative success of DFT+U warrants exploration of thermal transport and other observables within this level of theory.Physical Review Materials 3, 065405 (2019).[54] M.

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Section: Computational Detailsmentioning

confidence: 99%

Capturing the ground state of uranium dioxide from first principles: crystal distortion, magnetic structure, and phonons

Zhou¹,

Ma²,

Xiao³

et al. 2022

Preprint

Self Cite

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“…This means that training EIPs by using IDs dramatically deceases the amount of training data, thus further speeding up the process. We also considered strain derivatives formally defined as second-order irreducible strain derivatives of energy in a cubic system, defined by [43]:…”

Section: B Ifc From Irreducible Derivativesmentioning

confidence: 99%

“…Our training data were obtained from DFT calculations carried out via a projector augmented-wave (PAW) method [45,46], as implemented in the Vienna ab initio simulation package (VASP) [47,48]. The strongly constrained and appropriately normed (SCAN) [49] functional was used as the exchange correlation functional, as it provides phonon dispersion and thermal conductivity estimates that show good agreement with experiments conducted on ThO 2 [15,43,50]. SCAN calculations employ PAW potentials generated using the Perdew, Burke, Ernzerhof generalized gradient approximation (GGA) functional [51].…”

Section: Training and Validationmentioning

confidence: 99%

“…Importantly, these properties were not used in the fitting and thus aid in ascertaining the predictive capabilities of the PW. Table V lists the calculated elastic constants, comparing with experiments from Clausen et al [62], Macedo et al [63], and Khanolkar et al [43,64]; Figure 1 presents the calculated phonon spectra, as compared with experiments from Bryan et al [44]; Figure 2 gives the calculated thermal conductivity, as compared with experiments from Xiao et al [50], Muta et al [65], and Bakker et al [66].…”

Section: B Phonon Propertiesmentioning

confidence: 99%

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Improving empirical interatomic potentials for predicting thermophysical properties by using an irreducible derivatives approach: The case of thorium dioxide

Zhou¹,

Jiang²,

Xiao³

et al. 2022

Preprint

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The accuracy of physical property predictions using classical molecular dynamics simulations is determined by the quality of the empirical interatomic potentials (EIPs). We introduce a training approach for EIPs, based on direct comparisons of the second-and third-order interatomic force constants (IFCs) between EIP and density functional theory (DFT) calculations. This work's unique aspect is the utilization of irreducible derivatives (IDs) of the total energy, which leverage on the symmetry of the crystalline structure and provide a minimal representation of the IFCs. Our approach is tailored toward accurate predictions of thermal conductivity, thus requiring knowledge of both harmonic and anharmonic IFCs by matching second-and third-order displacement derivatives, whereas second-order strain derivatives are needed for determining the elastic constants. We demonstrate this approach as an efficient and robust manner in which to train EIPs for predicting phonons and related properties, by optimizing parameters of an embedded-atom method potential for ThO2, which is used as a model system for fluorite oxides. Our ID-trained EIP provides thermophysical properties in great agreement with DFT, and outperforms previously widely utilized EIP for ThO2 in phonon dispersion and thermal conductivity calculations. It also provides reasonable estimates of thermal expansion and the formation energies of simple defects.

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The generalized quasiharmonic approximation via space group irreducible derivatives

Cited by 2 publications

References 74 publications

Capturing the ground state of uranium dioxide from first principles: crystal distortion, magnetic structure, and phonons

Capturing the ground state of uranium dioxide from first principles: crystal distortion, magnetic structure, and phonons

Improving empirical interatomic potentials for predicting thermophysical properties by using an irreducible derivatives approach: The case of thorium dioxide

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