Modelling the enthalpy change and transition temperature dependence of the metal–insulator transition in pure and doped vanadium dioxide

Abstract

We show that a non-collinear spin density GGA+U functional calculation can describe the enthalpy difference (latent heat) of ΔE0 = −44.2 meV per formula unit, similar to the experimental value, between the paramagnetic rutile and the M1 phases of VO2.

Hybrid band offset calculation for heterojunction interfaces between disparate semiconductors

“…21 However, it was recently noted that hybrid functionals over-estimate the gap of the lowtemperature phase, also resulting in incorrect magnetic ordering. [22][23][24][25] These problems could be minimized by using a smaller empirical fraction of Hartree-Fock exchange, a $ 0.10 or less, rather than the standard value of a ¼ 0.25. [22][23][24][25][26][27] Thus, a typical VO 2 interface calculation would need to use different values of a on each side of the interface.…”

“…A correct value of the R-M1 phase free energy difference or "latent heat" is critical for a correct microscopic description of the Mott-FET. 25 The calculations use the plane wave code CASTEP 30 with normconserving pseudopotentials and a plane wave cutoff energy of 680 eV, which converged total energy differences to 1 meV/atom. A 5 Â 5 Â 1 k-point mesh was adopted in the calculation.…”

Study of electronic phenomena in strongly correlated systems by use of ultrashort laser pulses

“…The description of structural modifications imposed by the inclusion of Mg is elucidated by DFT calculations in the work of Zhou [75]. Therein, the alternate structural arrangement is found to ensue from effects caused by O-vacancies, essential for valence satisfaction in the compound [75,79], rather than from V substitution by Mg. The interatomic distances of V-V pairs changes due to displacement of neighboring atoms, a result of the O-vacancies.…”

“…1.11), as a consequence, the differences in atomic arrangement are diminished [75] 7 . This is reflected in reduction of the latent energy required for the structural phase transition which leads in lowering of the T c [79], the latter can be calculated via the latent heat [79,80].…”

“…The theoretical studies of Lu [49,79] employing the VASP [81,82] and CASTEP [50,83] programs in conjunction with the GCA+U method, have established that the band gap arises from spin coupling at the dimerized chains in the monoclinic phase [49], in agreement with experimental results [67]. It is shown that the AFM spin order in the M1 phase is key to open the gap, whereas the R phase is paramagnetic 7 Lattice constants of the modified structures are available in reference [75] Figure 1.11: Structural modification brought forth by Mg substitution at the V sites for the rutile, R, phase (left) and monoclinic, M1, phase (right).…”