Density functional theory molecular calculations

The molecular interpretation of major topics in catalytic kinetics will be highlighted based on insights on the properties of transition-state intermediates as deduced from computational chemical density functional theory (DFT) calculations. 

Of course, experimental methods are used to determine the molecular properties of 1,2,4-triazoles but computational studies, particularly density functional theory (DFT) calculations, are frequently carried out to predict and confirm the experimental findings. Calculation of the fundamental vibrational frequencies using the 6-311G(d,p) basis set has been used to support a comprehensive study of the vibrational spectra of 1,2,4-triazole <2000JST(530)183>. 

Fig. 5 A proposed mechanism for enhanced emission (or AIEE) in solid-state organic dye nanoparticles. The dye considered here is trans-biphenylethylene (CN-MBE) compound. The geometry is optimized by the density functional theory (DFT) calculation at the B3LYP/6-31G level. Molecular distortion such as twisting and/or subsequent planarization causes prevention of radiationless processes along with specific aggregation such as the /-aggregate in the nanoparticles...

Molecular-level studies of mechanisms of proton and water transport in PEMs require quantum mechanical calculations these mechanisms determine the conductance of water-filled nanosized pathways in PEMs. Also at molecular to nanoscopic scale, elementary steps of molecular adsorption, surface diffusion, charge transfer, recombination, and desorption proceed on the surfaces of nanoscale catalyst particles these fundamental processes control the electrocatalytic activity of the accessible catalyst surface. Studies of stable conformations of supported nanoparticles as well as of the processes on their surface require density functional theory (DFT) calculations, molecular... 

It is essential to have tools that allow studies of the electronic structure of adsorbates in a molecular orbital picture. In the following, we will demonstrate how we can use X-ray and electron spectroscopies together with Density Functional Theory (DFT) calculations to obtain an understanding of the local electronic structure and chemical bonding of adsorbates on metal surfaces. The goal is to use molecular orbital theory and relate the chemical bond formation to perturbations of the orbital structure of the free molecule. This chapter is complementary to Chapter 4, which... 

Figure 6.2 Results of molecular mechanics (MM) simulation (top) and density functional theory (DFT) calculation (bottom).

Density functional theory (DFT) calculations were also carried out to assign the molecular orbitals involved in the transitions that lead to luminescence, concluding that metal centered (du )1(pu)1 or (da )1 (pa)1 excited states are responsible for the luminescence in the solid state, while in dilute solutions the luminescence arises from ira excited states in the pentafluorophenyl ligands or from ir-MMCT transitions. 

The molecular geometries and the frontier orbital energies of heterophospholes 28-31 were obtained from density functional theory (DFT) calculations at the B3LYP/6-311- -G, level. The 1,3-dipolar cycloaddition reactivity of these heterophospholes in reactions with diazo compounds was evaluated from frontier molecular orbital (FMO) theory. Among the different types of heterophospholes considered, the 2-acyl-l,2,3-diazaphosphole 28, 377-1,2,3,4-triazaphosphole 30, and 1,3,4-thiazaphosphole 31 were predicted to have the highest dipolarophilic reactivities. These conclusions are in qualitative agreement with available experimental results <2003JP0504>. 

Square-planar bis(dithiolene) complexes have also been the subject of theoretical investigations (43-46). For example, density functional theory (DFT) calculations indicated that the highest occupied molecular orbital (HOMO) for Ni(S2C2H2)2 is primarily a ligand-based orbital comprising of four 3pz orbitals of sulfur, perpendicular to the molecular xy plane, and four 2p-orbitals of carbon with opposite phases. The lowest unoccupied molecular orbital (LUMO) is a mix of ligand-metal orbitals, but still mostly of the ligand... 

Density functional theory (DFT) calculations of two types of push-pull chromophores built around thiophene-based 7t-conjugating spacers rigidified by either covalent bonds or noncovalent intramolecular interactions (Figure 6) have been carried out to assign the relevant electronic and vibrational features and to derive useful information about the molecular structure of these NLO-phores <2003CEJ3670>. 

Density functional theory (DFT) calculations at the B3LYP/6-31H-G"" level were carried out on the 1,3-dipolar cycloadditions of various heterophospholes, including 1,3-azaphosphole, with diazo compounds across the P=N bond <2003JP0504>. In most cases, the dominant frontier orbital interaction is between HOMO(diazo) with LUMO(heterophosphole) however, 1,3-azaphosphole has a HOMO of high energy and for it, HOMO(heterophosphole)-LUMO(diazo) is also important (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital). 

Fock molecular orbital (HF-MO), Generalized Valence Bond (GVB) [49,50] and the Complete Active Space Self-consistent Filed (CASSCF) [50,51], and full Cl methods. [51] Density Functional Theory (DFT) calculations [52-54] are also incorporated into AIMD. One way to perform liquid-state AIMD simulations, is presented in the paper by Hedman and Laaksonen, [55], who simulated liquid water using a parallel computer. Each molecule and its neighbors, kept in the Verlet neighborlists, were treated as clusters and calculated simultaneously on different processors by invoking the standard periodic boundary conditions and minimum image convention. 

The objective of the present work is to study the interaction between Hz and a Pd-decorated monolayer of graphene by means of density functional theory (DFT) calculations. First, we investigated the preferential adsorption geometry for molecular and dissociative versions, and then we revise the evolution of the chemical bonds during the adsorption process. 

Our previous work has shown that spin-coated films of zinc phthalocyanines exhibited detectable shifts in the optical absorption spectra during alcohol vapor exposure [5], We here report an investigation of the molecular interactions between zinc phthalocyanines and alcohols by the x-ray absorption spectroscopy, the phase contrast optical microscopy and the transmission electron microscopy. The experimental results are also compared with our Density Functional Theory (DFT) calculations of the interactions between alcohol molecules and the zinc atom of the phthalocyanines [5],... 

Latterly, increasing use has also been made of Quantum Molecular Dynamics (QMD), based on the pioneering work of Car and Parrinello (1985) (see Chapter 8). The Car-Parrinello method makes use of Density Functional Theory to calculate explicitly the energy of a system and hence the interatomic forces, which are then used to determine the atomic trajectories and related dynamic properties, in the manner of classical MD. As an ab initio technique, QMD has the advantage over classical simulation methods that it is not reliant on interatomic potentials, and should in principle lead to far more accurate results. The disadvantage is that it demands far greater computing resources, and its application has thus far been limited to relatively simple systems. 

One recent example of such studies is that of Senda et al.91 who studied liquid Li-Na alloys. They considered a cell containing 61 Li atoms and 39 Na atoms, thus modelling a Lio.6iNao.39 alloy. Subsequently, they applied a molecular dynamics method based on the density-functional theory in calculating the structure of the system for different temperatures. 

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