Comment on 'Quantum Backreaction on "Classical" Variables'

It is argued that the bracket of Anderson's canonical theory should have been antisymmetric otherwise serious controversies arise like violation of both hermiticity and the Leibniz rule of differentiation.Comment: 3 pages, LaTe

Performance of the modified Becke-Johnson potential

Very recently, in the 2011 version of the Wien2K code, the long standing shortcome of the codes based on Density Functional Theory, namely, its impossibility to account for the experimental band gap value of semiconductors, was overcome. The novelty is the introduction of a new exchange and correlation potential, the modified Becke-Johnson potential (mBJLDA). In this paper, we report our detailed analysis of this recent work. We calculated using this code, the band structure of forty one semiconductors and found an important improvement in the overall agreement with experiment as Tran and Blaha [{\em Phys. Rev. Lett.} 102, 226401 (2009)] did before for a more reduced set of semiconductors. We find, nevertheless, within this enhanced set, that the deviation from the experimental gap value can reach even much more than 20%, in some cases. Furthermore, since there is no exchange and correlation energy term from which the mBJLDA potential can be deduced, a direct optimization procedure to get the lattice parameter in a consistent way is not possible as in the usual theory. These authors suggest that a LDA or a GGA optimization procedure is used previous to a band structure calculation and the resulting lattice parameter introduced into the 2011 code. This choice is important since small percentage differences in the lattice parameter can give rise to quite higher percentage deviations from experiment in the predicted band gap value.Comment: 10 pages, 2 figures, 5 Table

A trion in a magnetic field revisited

We revisit the problem of a two dimensional trion in an external magnetic field. We demonstrate that the approximations used previously for finding the energy spectrum of this system break down in the experimentally accessible range of magnetic fields. It is shown that the neglect of the Coulomb-induced mixing of different Landau levels corresponding to non-interacting particles leads to a strong underestimation of the trion binding energies even at extremely high magnetic fields (hundreds of Tesla). Moreover, proper account of the Coulomb effects for certain values of the parameters can lead to the appearance of additional discrete trion states which were overlooked previously. Finally, we provide a database of the matrix elements necessary for calculation of the magnetotrion spectra for a wide class of materials