arXiv subjects

Mark Pederson

Publications and source records attributed to Mark Pederson.

3 recordsLinked to original sources

arXiv2010

First-principle studies of spin-electric coupling in a $\{Cu_3\}$ single molecular magnet

We report on a study of the electronic and magnetic properties of the triangular antiferromagnetic $\{Cu_3\}$ single-molecule magnet, based on spin density functional theory. Our calculations show that the low-energy magnetic properties are correctly described by an effective three-site spin $s=1/2$ Heisenberg model, with an antiferromagnetic exchange coupling $J \approx 5$ meV. The ground state manifold of the model is composed of two degenerate spin $S=1/2$ doublets of opposite chirality. Due to lack of inversion symmetry in the molecule these two states are coupled by an external electric field, even when spin-orbit interaction is absent. The spin-electric coupling can be viewed as originating from a modified exchange constant $δJ$ induced by the electric field. We find that the calculated transition rate between the chiral states yields an effective electric dipole moment $d = 3.38\times 10^{-33} {\rm C\ m} \approx e 10^{-4}a$, where $a$ is the Cu separation. For external electric fields ${\varepsilon} \approx 10^8$ V/m this value corresponds to a Rabi time $τ\approx 1$ ns and to a $δJ$ of the order of a few $μ$eV.

cond-mat.mes-hall↗

arXiv2004

Evolution of Electronic and Vibrational Polarity of NaF Nanocrystals from Diatomic to Bulk: A Density Functional Study

Density functional theory (DFT) is used to study vibrations, electrical dipole moments, and polarizabilities of NaF clusters. Because of prior experimental and theoretical studies, this is a good model system for tracking the evolution of the properties from diatomic molecule to bulk crystal. The ratio of vibrational to electronic contributions to the polarizability increases dramatically with size N in the closed shell clusters (NaF)_N. The open shell system Na_14F_13 has a greatly enhanced electronic polarizability. Contrary to previous studies on this system which treated only the outer electron by quantum mechanics, we find the O_h cubic structure to be stable relative to the polar distorted structures such as C_3v.

cond-mat.other↗

arXiv2003

Jahn-Teller instability in C6H6+ and C6H6- revisited

The benzene cation (C6H6+) has a doublet (e_{1g}) ground state in hexagonal ring (D_{6h}) geometry. Therefore a Jahn-Teller (JT) distortion will lower the energy. The present theoretical study yields a model Huckel-type Hamiltonian that includes the JT coupling of the e_{1g} electronic ground state with the two e_{2g} vibrational modes: in-plane ring-bending and C-C bond-stretching. We obtain the JT couplings from density functional theory (DFT), which gives a JT energy lowering of 970 cm^{-1} in agreement with previous quantum chemistry calculations. We find a non-adiabatic solution for vibrational spectra and predict frequencies shifts of both the benzene cation and anion, and give a reinterpretation of the available experimental data.

cond-mat↗