Density functional theory potential energy surfaces

Assuming that substituted Sb at the surface may work as catalytic active site as well as W, First-principles density functional theory (DFT) calculations were performed with Becke-Perdew [7, 9] functional to evaluate the binding energy between p-xylene and catalyst. Scalar relativistic effects were treated with the energy-consistent pseudo-potentials for W and Sb. However, the binding strength with p-xylene is much weaker for Sb (0.6 eV) than for W (2.4 eV), as shown in Fig. 4. 

Figure 6.35. Potential energy diagrams for adsorption and dissociation of N2on a Ru(0001) surface and on the same surface with a monoatomic step, as calculated with a density functional theory procedure. [Adapted from S. Dahl, A. Logadottir, R. Egberg, J. Larsen, I. Chorkendorff,...

While in previous ab initio smdies the reconstructed surface was mostly simulated as Au(lll), Feng et al. [2005] have recently performed periodic density functional theory (DFT) calculations on a realistic system in which they used a (5 x 1) unit cell and added an additional atom to the first surface layer. In their calculations, the electrode potential was included by charging the slab and placing a reference electrode (with the counter charge) in the middle of the vacuum region. From the surface free energy curves, which were evaluated on the basis of experimentally measured capacities, they concluded that there is no necessity for specific ion adsorption [Bohnen and Kolb, 1998] and that the positive surface charge alone would be sufficient to lift the reconstmction. 

However, even the best experimental technique typically does not provide a detailed mechanistic picture of a chemical reaction. Computational quantum chemical methods such as the ab initio molecular orbital and density functional theory (DFT) " methods allow chemists to obtain a detailed picture of reaction potential energy surfaces and to elucidate important reaction-driving forces. Moreover, these methods can provide valuable kinetic and thermodynamic information (i.e., heats of formation, enthalpies, and free energies) for reactions and species for which reactivity and conditions make experiments difficult, thereby providing a powerful means to complement experimental data. 

Seifert, G., Kruger, K., 1995, Density Functional Theory, Calculations of Potential Energy Surfaces and Reaction Paths in The Reaction Path in Chemistry Current Approaches and Perspectives, Heidrich, D. (ed.), Kluwer, Amsterdam. 

Lelj, F., C. Adamo, and V. Barone. 1994. Role of Hartree-Fock exchange in density functional theory. Some aspects of the conformational potential energy surface of glycine in the gas phase. Chem. Phys. Lett. 230, 189. 

Deng, L., V. Branchadell, and T. Ziegler. 1994. Potential Energy Surface of the Gas-Phase Sn2 Reactions X + CH2X = XCH3 + X- (X = F, Cl, Br, I) A Comparative Study by Density Functional Theory and ab initio Methods. 

The DECP model successfully explained the observed initial phase of the fully symmetric phonons in a number of opaque crystals [24]. The absence of the Eg mode was attributed to an exclusive coupling between the electrons photoexcited near the r point and the fully symmetric phonons. A recent density functional theory (DFT) calculation [23] demonstrated this exclusive coupling as the potential energy surface (Fig. 2.4). The minimum of the potential surface of the excited state shifted significantly along the trigonal (z) axis,... 

Ab initio calculations and density functional theory studies of the gas-phase addition of HF to CH2=CH2 have revealed the possibility of forming trimolecular (two HF and one ethylene) and dimolecular (one FIF and one ethylene) complexes and transition-state structures and of the catalytic effect of the second molecule of the reagent. An energetically favourable pathway was selected on the basis of the computed potential-energy surface for these two reactions. ... 

Phenylperoxy radical has similarly been a topic of experimental and theoretical interest. Tokmakov et al. " calculated a potential energy surface for phenyl radical and O2 using ab initio G2(MP2) calculations. Weisman and Head-Gordon used time-dependent density functional theory (TD-DFT) calculations to examine the effect of substituents on the phenylperoxy radical s UV-vis absorption spectrum. " Lin and Mebel used ab initio methods to study the phenoxy radical -f O-atom reaction. "... 

By using a full panoply of theory—time-dependent density functional theory and CASSCF and CASMP2 ab initio methods—the states and potential-energy surface features associated with the dynamics were uncovered. The high-energy excitation of acetone gives several excited Rydberg states that reach the S2( , 3i) surface in... 

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