Clusters optimization calculations

In order to interpret the results of our experiments, optimal-control calculations were performed where a GA controlled 40 independent degrees of freedom in the laser pulses that were used in a molecular dynamics simulation of the laser-cluster interactions for Xejv clusters with sizes ranging from 108 to 5056 atoms/cluster. These calculations, which are reported in detail elsewhere [67], showed optimization of the laser-cluster interactions by a sequence of as many as three laser pulses. Detailed inspection of the simulations revealed that the first pulse in this sequence initiates the cluster ionization and starts the expansion of the cluster, while the second and third pulse optimize two mechanisms that are directly related to the behaviour of the electrons in the cluster. We consistently observe that the second pulse in the three-pulse sequence arrives a time delay where the conditions for enhanced ionization are met. In other words, the second pulse arrives at a time where the ionization of atoms is assisted by the proximity of surrounding ions. The third peak is consistently observed at a delay where the collective oscillation of the quasi-free electrons in the cluster is 7t/2 out of phase with respect to the driving laser field. For a driven and damped oscillator this phase-delay represents an optimum for the energy transfer from the driving force to the oscillator. 

To understand these highly interesting photophysical properties of nucleobases, we have carried out CIS and coupled cluster (CC) calculations of the potential energy profiles of cytosine and its derivatives at optimized CIS geometries [10]. The results indicate that the Sj S0 internal conversion occurs through a barrierless state switch from the initially excited 1 tttt state to a biradical state, which intersects... 

The FIR spectrum of acetone, in gas phase, has been studied by several authors [60,61]. Two peaks with some substructure are observed around 125 cm and 105 cm. Using the potential energy fuction (114), as well as the geometry obtained in a full optimization calculation, two clusters of transitions of appreciable intensities are obtained theoretically. The first one occurs between the torsional microstates A A2, G — G, E — E and E — E. The second cluster corresponds to an overtone between the microstates Ei — E, E4 — E3, G — G and A2 — Ai. 

Figure 1. Ag2 adsorption on rutile (110) models for cluster model calculations. Structures a to c are optimized, d to f are initial atructures. - Ti, - O, - Ca, - Ag.

After generating optimized clusters, the intermolecular interaction energies between pair molecules a and / ( ) in the cluster were calculated using the supermolecular approach ... 

The Pariser-Parr-Pople Hamiltonian for the description of the 7i-electrons in trans-polyacetylene is reparametrized using ab initio Coupled Cluster Doubles calculations based on a Restricted Hartree Fock reference on trans-butadiene. To avoid the spin contaminations inherent in Unrestricted Hartree Fock (UHF) type calculations on polymethine chains in the doublet state the Annihilated Unrestricted Hartree Fock (AUHF) model is applied in our PPP calculations (tPA (CH) , polyenes H-(CH)2N-H, polymethines H-(CH)2N+1-H). In geometry optimizations on polymethine chains it is shown that in contrast to results from Hiickel type models the width of neutral solitons is strongly... 

Figure 4. The 3x3x3 and 3 X 3 X 4 fee erystallite structures proposed by Pilgrim and Duncan for intermediate sized Ti/C and Zr/C magic number clusters and the structure of the Tii4Ci3 neutral cluster optimized by Dance from DFT calculations (Ti -C = 2.13 A, Ti5-C = 2.17 A, 713-0 = 2.05 A Ti -Ti = 3.02 A, Ti3-Ti3 = 2.89 A the superscripts are the coordination numbers, that is the number of bonds with atoms of the other element). Reproduced with permission from the authors.

The CCSD(F12) model as well as the full CCSD-F12 approach and other simplifications of it are currently being implemented in various quantum chemistry programs [59, 61, 62, 71, 72, 73, 74, 75, 76, 77, 78, 79], also in combination with connected triples and higher excitations. In particular Kohn and co-workers [72] have shown that the CCSD(F12) model is an excellent approximation to the full CCSD-F12 approach, and the CCSD(F12) model is the method of choice that we have implemented in the Turbomole program. The present work reports on one of the first applications of CCSD(F12) theory" with chemical relevance. In such a real-life application, CCSD(F12) calculations are combined with a series of other coupled-cluster calculations including geometry optimizations, calculations of harmonic vibrational frequencies, and coupled-cluster calculations with connected triples and quadruples. Within the whole set of calculations that must be performed, the CCSD(F12) calculations take only a fraction of the total computation time, and therefore, in an application as the one presented here, there appears to be no need to further simplify the CCSD(F12) model. 

The ab initio QM technique can be used to determine optimal structmes of molecular clusters and to calculate energies for any single geometry of the cluster. QM calculations provide molecular wave functions, which can be used to derive physicochemical properties, such... 

Figure 4.29. Back-calculated results for files VALIDX.dat. The data are presented sequentially from left to right. The ordinate is in % of the nominal concentration. Numbers X = 1,2, and 3 indicate the data file. Each bracket indicates a day s worth of results (sorted by concentration). The log/log format tends to produce positive deviations at low concentrations, while the lin/lin format does the opposite, to the point of suggesting negative concentrations The reason is that the low concentration values are tightly clustered at the left end of the lin/lin depiction whereas the values are evenly spread in the log/log depiction, with commensurate effects on the position of Xmean, the sum Sxx< and the influence each coordinate has on the slope. The calibration design was optimized for the log/log format.

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