The quantum phases of 2-leg spin-1/2 ladders with skewed rungs are obtained using exact diagonalization of systems with up to 26 spins and by density matrix renormalization group calculations to 500 spins. The ladders have isotropic antiferromagnetic (AF) exchange J2 > 0 between first neighbors in the legs, variable isotropic AF exchange J1 between some first neighbors in different legs, and an unpaired spin per odd-membered ring when J1 J2. Ladders with skewed rungs and variable J1 have frustrated AF interactions leading to multiple quantum phases: AF at small J1, either F or AF at large J1, as well as bond-order-wave phases or reentrant AF (singlet) phases at intermediate J1.

There is a resurgence of interest in the electronic structure of perylene for its applications in molecular devices such as organic photovoltaics and organic light emitting diodes. In this study, we have obtained the low-lying singlet states of perylene by exactly solving the Parisar-Parr-Pople model Hamiltonian of this system with 20 sites and 20 electrons, in the VB basis where dimensionality is ∼ 5.92 billion. The triplet states of perylene are obtained using a DMRG scheme with symmetry adaptation. The one and two photon states are very close in energy ∼ 3.2 eV while the lowest triplet state is slightly below 1.6 eV indicating that perylene is a good candidate for singlet fission.To explore the tunability of the electronic states, we have studied donor-acceptor substituted perylenes. The two donors and two acceptors are substituted symmetrically either at the four bay sites or four peri sites. In all the bay substitution and one peri substitution at moderate D/A strength, the optical gap is lowered to about 2.8 eV. 1 arXiv:1809.05909v1 [cond-mat.str-el] 16 Sep 2018These molecules can be used as blue emitters. We have also reported bond orders in all the cases and perylene as well as substituted perylenes can be viewed as two weakly coupled naphthalene in the singlet states but in triplets these bonds tend to be comparable to other bonds in strength. The charge densities in substituted perylenes are mostly localized around the substitution sites in the ground state. The positive spin densities in triplets are concentrated around the peri and bay sites with the remaining sites having small spin densities of either sign.

In recent years Polycyclic Aromatic Hydrocarbons (PAHs) have been studied for their electronic properties as they are viewed as nanodots of graphene. They have also been of interest as functional molecules for applications such as light emitting diodes and solar cells.Since last few years varying structural and chemical properties corresponding to the size and geometry of these molecules have been studied both theoretically and experimentally.In this paper, we carry out a systematic study of the electronic states of several PAHs using the Pariser-Parr-Pople model which incorporates long-range electron correlations. In all the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than one-half of the singlet-singlet gap in all cases and hence none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states which include bond orders and spin densities (in triplets) of these systems.

We report in this paper the dynamical properties of GdMn 2 O 5 studied by inelastic neutron scattering and infrared spectroscopy assisted by ab initio calculations. Our work sheds light on the electromagnon, a magnetic mode that can be excited by an electric field. Combining spin-wave measurements, simulations, and ab initio calculations of the single-ion anisotropies and the superexchange interactions, we describe in detail the magnetic contribution to this mode. An exhaustive study of the temperature and polarization dependence of its electroactivity completes this comprehensive study of the complex GdMn 2 O 5 system.

<div><div><div><div><p>The smallest magnetic aromatic hydrocarbons reported to date consist of at least six fused- azulene. In order to determine the magnetic state of a given molecule computationally- demanding state-of-the-art methods, such as DMRG or DFT, are required. We introduce a simple computational procedure to screen large sets of molecules and identify likely can- didates worthy of more sophisticated (and costly) analysis. We consider smaller molecules that combine azulene and naphtalene and find two new magnetic molecules.</p></div></div></div></div>