Improving the Description of Nonmagnetic and Magnetic Molecular Crystals via the van der Waals Density Functional

Abstract

We have derived and implemented a stress tensor formulation for the van der Waals density functional (vdW-DF) with spin-polarization-dependent gradient correction (GC) recently proposed by the authors [J. Phys. Soc. Jpn. 82, 093701 (2013)] and applied it to nonmagnetic and magnetic molecular crystals under ambient condition. We found that the cell parameters of the molecular crystals obtained with vdW-DF show an overall improvement compared with those obtained using local density and generalized gradient approximations.In particular, the original vdW-DF with GC gives the equilibrium structural parameters of solid oxygen in the α-phase, which are in good agreement with the experiment.

Molecular Interactions for Modeling of Oxygen System Using van der Waals Density Functional Approach

“…and the number of mesh is set 31. We have already confirmed a reliability of these parameters by realizing the previous results [8,[18][19][20]. The molecular configurations of T-type, X-type, and S-type are shown in Fig.…”

First-principles description of van der Waals bonded spin-polarized systems using the vdW-DF+ U method: Application to solid oxygen at low pressure

“…In a broader context, we reiterate the notion first given in Ref. 5: this approach is a clear step forward in quantitative prediction of magnetic and structural properties in systems where vdW and spin-spin interaction compete, such as molecular magnets and metalorganic systems. Application of this approach to study of molecular spintronics is highly anticipated.…”

“…However, due to the subtle balance of vdW and exchange interactions mentioned earlier, satisfactory description of solid O 2 from first principles is quite challenging; in fact, it may be considered one of the most critical benchmarks for measuring the predictive capability of electronic structure methods 5 . The local and semilocal approximations to the density functional [e.g., the local spin density approximation (LSDA) and the generalized gradient approximation (GGA)] used conventionally in the Kohn-Sham method of density functional theory (DFT) fail rather miserably in predicting the structure of the low-temperature ground state monoclinic (α) phase (Fig.…”

“…For example, the vdW-DF functional of Langreth, Lundqvist, and coworkers 6 has been shown to perform adequately in terms of predicting the volume of the unit cell, but the problem remains in predicting the shape of the unit cell; the calculated lattice parameters are off by as large as 20% compared to experiment 7 . The poor performance of these functionals was suggested to be due to overestimation of bonding in the antiferromagnetic molecule pairs compared to ferromagnetic pairs 5,7 . The magnetic interaction J is proportional to −t 2 /∆E, where t is the transfer integral between sites, ∆E is the energy gap separating the spin-up and spin-down states sandwiching the Fermi level, and J is taken to be negative for antiferromagnetic coupling.…”

“…GGAs are known to underestimate ∆E and overestimate |t|, so it is not surprising that the antiferromagnetic interaction is overestimated. vdW-DF does not improve much in this regard, so Obata and coworkers opted to consider a spin-polarization dependent gradient correction to be used in combination with vdW-DF 5,7 . In their approach, two scaling parameters for relative spin polarization and spin-dependent gradient correction were introduced in the vdW-DF-SGC method, and the errors in the magnetic interaction were corrected to some extent depending on the chosen parameters.…”