Search results for "Coupled"

State-of-the-art density matrix renormalization group and coupled cluster theory studies of the nitrogen binding curve.

2004

We study the nitrogen binding curve with the density matrix renormalization group (DMRG) and single-reference and multireference coupled cluster (CC) theory. Our DMRG calculations use up to 4000 states and our single-reference CC calculations include up to full connected hextuple excitations. Using the DMRG, we compute an all-electron benchmark nitrogen binding curve, at the polarized, valence double-zeta level (28 basis functions), with an estimated accuracy of 0.03mE_h. We also assess the performance of more approximate DMRG and CC theories across the nitrogen curve. We provide an analysis of the relative strengths and merits of the DMRG and CC theory under different correlation condition…

Communication: Restoring full size extensivity in internally contracted multireference coupled cluster theory.

2012

The reason for the lack of size extensivity in the valence space in current implementations of internally contracted multireference coupled cluster theories is the procedure used to eliminate redundant components from the cluster operator. We present a simple way to restore full size extensivity by performing this critical step in a basis of excitation operators that are normal ordered with respect to the multiconfigurational reference function.

Grating-assisted third-harmonic generation in photonic crystal fibers using a pulse pump

2011

We demonstrate that quasi-phase-matching of the third-harmonic generation process can be obtained for a pulse pump in the photonic crystal fiber with a refractive-index grating. Conversion efficiency is calculated numerically using a system of coupled generalized nonlinear Schrodinger equations. We propose a special design of the microstructured fiber for the third-harmonic generation and analyze different phenomena limiting the maximum efficiency for short (femtosecond) and long (picosecond) pump pulses. Moreover, we show that a certain level of a group-velocity mismatch between the pump and the third harmonic can increase the maximum efficiency in the long pulse regime.

Triple excitation effects in coupled-cluster calculations of frequency-dependent hyperpolarizabilities

1998

Abstract We describe an implementation of an analytic scheme for the calculation of static and dynamical first hyperpolarizabilities at the CC3 level in the framework of coupled-cluster response theory. Calculations are reported for the static, the second harmonic generation, and the optical rectification hyperpolarizabilities of FH. The results indicate the importance of triple excitation effects for accurate theoretical predictions of hyperpolarizabilities and lend further support to previous contentions that an experimental value for the second harmonic generation hyperpolarizabilities of FH should be reconsidered.

Linear and nonlinear optical properties of some organoxenon derivatives

2007

We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2…

Lower Rydberg series of methane: a combined coupled cluster linear response and molecular quantum defect orbital calculation.

2006

Vertical excitation energies as well as related absolute photoabsorption oscillator strength data are very scarce in the literature for methane. In this study, we have characterized the three existing series of low-lying Rydberg states of CH4 by computing coupled cluster linear response (CCLR) vertical excitation energies together with oscillator strengths in the molecular-adapted quantum defect orbital formalism from a distorted Cs geometry selected on the basis of outer valence green function calculations. The present work provides a wide range of data of excitation energies and absolute oscillator strengths which correspond to the Rydberg series converging to the three lower ionization p…

In human and rat lung membranes [35s]GTPγS binding is a tool for pharmacological characterization of G protein-coupled devucleotide receptors

1999

The P2Y receptor family is activated by extracellular nucleotides such as ATP and UTP. P2Y receptors regulate physiological functions in numerous cell types. In lung, the P2Y2 receptor subtype plays a role in controlling Cl- and fluid transport. Besides ATP or UTP, also diadenosine tetraphosphate (Ap4A), a stable nucleotide, seems to be of physiological importance. In membrane preparations from human and rat lung we applied several diadenosine polyphosphates to investigate whether they act as agonists for G protein-coupled receptors. We assessed this by determining the stimulation of [35S]GTPgammaS binding. Stimulation of [35S]GTPgammaS binding to G proteins has already been successfully ap…

Chemical characterization of ancient potteries from Himera and Pestavecchia necropolis (Sicily, Italy) by Inductively Coupled Plasma–Optical Emission…

2011

Abstract Thirty-eight samples of pottery were analyzed for determining chemical composition in order to establish their provenance. The potteries tested in the present research come from Himera and Pestavecchia archaeological sites. After digestion in microwave oven, the samples have been analyzed for fourteen minor elements (Ba, Cd, Co, Cr, Cu, Ga, Li, Mn, Ni, Pb, Sr, Ti, Tl, and Zn) and six major elements (Al, Ca, Fe, K, Mg, and Na). Chemical analysis was carried out by Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES). The most abundant minor elements are Cr, Ba and Ni. Cr concentration ranged from 66 to 3635 mg kg − 1 , Ba concentration ranged from 388 to 2677 mg kg − 1…

Cover Feature: Single Peptide Backbone Surrogate Mutations to Regulate Angiotensin GPCR Subtype Selectivity (Chem. Eur. J. 47/2020)

2020

Single Peptide Backbone Surrogate Mutations to Regulate Angiotensin GPCR Subtype Selectivity

2020

Mutating the side-chains of amino acids in a peptide ligand, with unnatural amino acids, aiming to mitigate its short half-life is an established approach. However, it is hypothesized that mutating specific backbone peptide bonds with bioisosters can be exploited not only to enhance the proteolytic stability of parent peptides, but also to tune its receptor subtype selectivity. Towards this end, four [Y]6-Angiotensin II analogues are synthesized where amide bonds have been replaced by 1,4-disubstituted 1,2,3-triazole isosteres in four different backbone locations. All the analogues possessed enhanced stability in human plasma in comparison with the parent peptide, whereas only two of them a…