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Register a new userSimple way to apply nonlocal van der Waals functionals within all-electron methods
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The method based on fast Fourier transforms proposed by G. Roman-Perez and J. M. Soler [Phys. Rev. Lett. 103, 096102 (2009)], which allows for a computationally fast implementation of the nonlocal van der Waals (vdW) functionals, has significantly contributed to making the vdW functionals popular in solid-state physics. However, the Roman-Perez-Soler method relies on a plane-wave expansion of the electron density; therefore it can not be applied readily to all-electron densities for which an unaffordable number of plane waves would be required for an accurate expansion. In this work, we present the results for the lattice constant and binding energy of solids that were obtained by applying a smoothing procedure to the all-electron density calculated with the linearized augmented plane-wave method. The smoothing procedure has the advantages of being very simple to implement, basis-set independent, and allowing the calculation of the potential. It is also shown that the results agree very well with those from the literature that were obtained with the projector augmented wave method.
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The nonlocal van der Waals (NL-vdW) functionals [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] are being applied more and more frequently in solid-state physics, since they have shown to be much more reliable than the traditional semilocal functionals for systems where weak interactions play a major role. However, a certain number of NL-vdW functionals have been proposed during the last few years, such that it is not always clear which one should be used. In this work, an assessment of NL-vdW functionals is presented. Our test set consists of weakly bound solids, namely rare gases, layered systems like graphite, and molecular solids, but also strongly bound solids in order to provide a more general conclusion about the accuracy of NL-vdW functionals for extended systems. We found that among the tested functionals, rev-vdW-DF2 [Hamada, Phys. Rev. B 89, 121103(R) (2014)] is very accurate for weakly bound solids, but also quite reliable for strongly bound solids.
We present the idea and illustrate potential benefits of having a tool chain of closely related regular, unscreened and screened hybrid exchange-correlation (XC) functionals, all within the consistent formulation of the van der Waals density functional (vdW-DF) method [JPCM 32, 393001 (2020)]. Use of this chain of nonempirical XC functionals allows us to map when the inclusion of truly nonlocal exchange and of truly nonlocal correlation is important. Here we begin the mapping by addressing hard and soft material challenges: magnetic elements, perovskites, and biomolecular problems. We also predict the structure and polarization for a ferroelectric polymer. To facilitate this work and future broader explorations, we furthermore present a stress formulation for spin vdW-DF and illustrate use of a simple stability-modeling scheme to assert when the prediction of a soft mode (an imaginary-frequency vibrational mode, ubiquitous in perovskites and soft matter) implies a prediction of an actual low-temperature transformation.
The nonlocal correlation energy in the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004); Phys. Rev. B 76, 125112 (2007); Phys. Rev. B 89, 035412 (2014)] can be interpreted in terms of a coupling of zero-point energies of characteristic modes of semilocal exchange-correlation (xc) holes. These xc holes reflect the internal functional in the framework of the vdW-DF method [Phys. Rev. B 82, 081101(2010)]. We explore the internal xc hole components, showing that they share properties with those of the generalized-gradient approximation. We use these results to illustrate the nonlocality in the vdW-DF description and analyze the vdW-DF formulation of nonlocal correlation.
We report structural, physical properties and electronic structure of van der Waals (vdW) crystal VI3. Detailed analysis reveals that VI3 exhibits a structural transition from monoclinic C2/m to rhombohedral R-3 at Ts ~ 79 K, similar to CrX3 (X = Cl, Br, I). Below Ts, a long-range ferromagnetic (FM) transition emerges at Tc ~ 50 K. The local moment of V in VI3 is close to the high-spin state V3+ ion (S = 1). Theoretical calculation suggests that VI3 may be a Mott insulator with the band gap of about 0.84 eV. In addition, VI3 has a relative small interlayer binding energy and can be exfoliated easily down to few layers experimentally. Therefore, VI3 is a candidate of two-dimensional FM semiconductor. It also provides a novel platform to explore 2D magnetism and vdW heterostructures in S = 1 system.
The exfoliation of two naturally occurring van der Waals minerals, graphite and molybdenite, arouse an unprecedented level of interest by the scientific community and shaped a whole new field of research: 2D materials research. Several years later, the family of van der Waals materials that can be exfoliated to isolate 2D materials keeps growing, but most of them are synthetic. Interestingly, in nature plenty of naturally occurring van der Waals minerals can be found with a wide range of chemical compositions and crystal structures whose properties are mostly unexplored so far. This Perspective aims to provide an overview of different families of van der Waals minerals to stimulate their exploration in the 2D limit.
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