Myrta Grüning
University of Coimbra
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Myrta Grüning.
Computer Physics Communications | 2009
A. C. Marini; Conor Hogan; Myrta Grüning; Daniele Varsano
yambo is an ab initio code for calculating quasiparticle energies and optical properties of electronic systems within the framework of many-body perturbation theory and time-dependent density functional theory. Quasiparticle energies are calculated within the GW approximation for the self-energy. Optical properties are evaluated either by solving the Bethe-Salpeter equation or by using the adiabatic local density approximation. yambo is a plane-wave code that, although particularly suited for calculations of periodic bulk systems, has been applied to a large variety of physical systems. yambo relies on efficient numerical techniques devised to treat systems with reduced dimensionality, or with a large number of degrees of freedom. The code has a user-friendly command-line based interface, flexible 110 procedures and is interfaced to several publicly available density functional ground-state codes.
Journal of Chemical Physics | 2001
Myrta Grüning; O. V. Gritsenko; S. J. A. van Gisbergen; Evert Jan Baerends
Shape corrections to the standard approximate Kohn-Sham exchange-correlation (xc) potentials are considered with the aim to improve the excitation energies (especially for higher excitations) calculated with time-dependent density functional perturbation theory. A scheme of gradient-regulated connection (GRAC) of inner to outer parts of a model potential is developed. Asymptotic corrections based either on the potential of Fermi and Amaldi or van Leeuwen and Baerends (LB) are seamlessly connected to the (shifted) xc potential of Becke and Perdew (BP) with the GRAC procedure, and are employed to calculate the vertical excitation energies of the prototype molecules N2, CO, CH2O, C2H4, C5NH5, C6H6, Li2, Na2, K2. The results are compared with those of the alternative interpolation scheme of Tozer and Handy as well as with the results of the potential obtained with the statistical averaging of (model) orbital potentials. Various asymptotically corrected potentials produce high quality excitation energies, whic...
Journal of Chemical Physics | 2002
Myrta Grüning; O. V. Gritsenko; Stan J. A. van Gisbergen; Evert Jan Baerends
It is well known that shape corrections have to be applied to the local-density (LDA) and generalized gradient (GGA) approximations to the Kohn–Sham exchange–correlation potential in order to obtain reliable response properties in time dependent density functional theory calculations. Here we demonstrate that it is an oversimplified view that these shape corrections concern primarily the asymptotic part of the potential, and that they affect only Rydberg type transitions. The performance is assessed of two shape-corrected Kohn–Sham potentials, the gradient-regulated asymptotic connection procedure applied to the Becke–Perdew potential (BP–GRAC) and the statistical averaging of (model) orbital potentials (SAOP), versus LDA and GGA potentials, in molecular response calculations of the static average polarizability α, the Cauchy coefficient S−4, and the static average hyperpolarizability β. The nature of the distortions of the LDA/GGA potentials is highlighted and it is shown that they introduce many spuriou...
Nano Letters | 2009
Myrta Grüning; Andrea Marini; Xavier Gonze
Within the Tamm-Dancoff approximation, ab initio approaches describe excitons as packets of electron-hole pairs propagating only forward in time. However, we show that in nanoscale materials excitons and plasmons hybridize, creating exciton-plasmon states where the electron-hole pairs oscillate back and forth in time. Then, as exemplified by the trans-azobenzene molecule and the carbon nanotubes, the Tamm-Dancoff approximation yields errors larger than the accuracy claimed in ab initio calculations. Instead, we propose a general and efficient approach that avoids the Tamm-Dancoff approximation, correctly describes excitons, plasmons, and exciton-plasmon states, and provides a good agreement with experimental results.
Journal of Chemical Physics | 2002
Myrta Grüning; O. V. Gritsenko; Evert Jan Baerends
An approximate Kohn–Sham (KS) exchange potential vxσCEDA is developed, based on the common energy denominator approximation (CEDA) for the static orbital Green’s function, which preserves the essential structure of the density response function. vxσCEDA is an explicit functional of the occupied KS orbitals, which has the Slater vSσ and response vrespσCEDA potentials as its components. The latter exhibits the characteristic step structure with “diagonal” contributions from the orbital densities |ψiσ|2, as well as “off-diagonal” ones from the occupied–occupied orbital products ψiσψj(≠1)σ*. Comparison of the results of atomic and molecular ground-state CEDA calculations with those of the Krieger–Li–Iafrate (KLI), exact exchange (EXX), and Hartree–Fock (HF) methods show, that both KLI and CEDA potentials can be considered as very good analytical “closure approximations” to the exact KS exchange potential. The total CEDA and KLI energies nearly coincide with the EXX ones and the corresponding orbital energies ...
Journal of Chemical Physics | 2003
Myrta Grüning; O. V. Gritsenko; Evert Jan Baerends
The standard local density approximation and generalized gradient approximations fail to properly describe the dissociation of an electron pair bond, yielding large errors (on the order of 50 kcal/mol) at long bond distances. To remedy this failure, a self-consistent Kohn–Sham (KS) method is proposed with the exchange-correlation (xc) energy and potential depending on both occupied and virtual KS orbitals. The xc energy functional of Buijse and Baerends [Mol. Phys. 100, 401 (2002); Phys. Rev. Lett. 87, 133004 (2001)] is employed, which, based on an ansatz for the xc-hole amplitude, is able to reproduce the important dynamical and nondynamical effects of Coulomb correlation through the efficient use of virtual orbitals. Self-consistent calculations require the corresponding xc potential to be obtained, to which end the optimized effective potential (OEP) method is used within the common energy denominator approximation for the static orbital Green’s function. The problem of the asymptotic divergence of the...
Physical Review B | 2014
Myrta Grüning; Claudio Attaccalite
We study second harmonic generation in
Physical Review B | 2011
Claudio Attaccalite; Myrta Grüning; Andrea Marini
h
Journal of Computational Chemistry | 2003
Delano P. Chong; Myrta Grüning; Evert Jan Baerends
-BN and MoS
Physical Review B | 2010
Myrta Grüning; Riad Shaltaf; Gian-Marco Rignanese
{}_{2}