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Dissociation Mechanism of trichloroacetic acid (TCAA) in liquid water has been investigated using the Car-Parrinello molecular dynamics (CPMD). The simulations have been performed in 300 K. Structures, energies and proton trajectories have been determined. The CPMD results show that process of Dissociation Mechanism is the creation of multi-stable structures of ionics. We found that in liquid trichloroacetic acid the hydrogen bonds form a special lattice, which results in reorganization of the attitude of ions like Zundel and Eigen structure. We also studied the excess proton transport in water after dissociation of strong acid and set the average lifetime of each structures of recognize ions.
In this project, the results of the nature of the Dissociation Mechanism of trichloroacetic acid in liquid water on CPMD method level are presented for the first time. We also studied the excess proton transport in water after dissociation of strong acid and set the average lifetime of each structures of recognize ions. Understanding the dissociation mechanism of a acid in aqueous solution is of great importance not only for acid-base chemistry but also for understanding biological processes . It was reason to investigate the complexity of the process of dissociation of trichloroacetic acid in liquid water on molecular dynamics approach level. After the visit on HPC-Europa2 program I have got one scientific publication in progress with my host Dr Carole A. Morrison and we are going to sent this paper to the one of the american journals. The results and graphics presented in this report will be included in the publication.
 J. M. Park, A. Laio, M. Iannuzzi, and M. Parrinello. J. Am. Chem. Soc., 128:11318–11319, 2006.
Ceria CeO2 is well known as a key component of the automotive catalysts and efficient catalysts or support for a series of other catalytic process of great industrial and environmental interest. Some of the most important applications of these systems are related to their reactivity towards CO or CO2 in relation to reduction of pollutions and greenhouse gases. In addition, it is found experimentally as appropriate support for noble metal catalysts for several reactions directed to production or deep purification of hydrogen as environmentally friendly fuel in fuel cells. Some of these reactions as water-gas shift reaction and preferential oxidation of CO in hydrogen feed, include as a key step interaction of the ceria with carbon monoxide (CO) and carbon dioxide (CO2). Two features of ceria are found very important for the activity and performance of the support/catalyst: the size of ceria particle (the nanoparticles are found by several orders of magnitude more active that large particles) and the degree of oxidation/reduction of the sample. By this reason our computational investigation was based on ceria particle (Ce21O42) designed in the host group (instead of extended ceria surface used in the other computational studies). During the research stay we performed extensive calculations along the following directions:
1. Determination of preferable position for formation of oxygen vacancies on the ceria nanocluster and estimation of the energy for vacancy formation; 2. Interaction of CO and CO2 with ceria nanoparticle; 3. Interaction of platinum cluster (Pt8) with the ceria nanoparticle
The search for different positions of oxygen vacancies was started from the stoichiometric ceria nanocluster Ce21O42 by removal of selected oxygen atoms. Such removal of neutral oxygen atom leads to appearance of two Ce(III) ions from two Ce(IV) ions in the initial stoichiometric particle and one of the unclear issues in the preferred location of those Ce(III) centers. According to the calculated relative energies of the structures, the stability of the O vacancies decreases in the following order: sub-surface layer, surface, edge. The preferable location of the Ce(III) ions are neighbors of the O vacancy when it is on the surface or edge, or farther from it when it is sub-surface.
The interaction of the ceria nanoparticle with CO resulted in spontaneous formation of CO2 or of surface carbonate when the local structure of the particle is suitable. The energy for CO2 formation from CO (accompanied with formation of an oxygen vacancy on the cluster) is found between 0.8 and 1.5 eV. Interaction of CO2 with the catalyst’s surface also results in formation of carbonate species with different stability depending on the adsorption mode of the carbonate and its location (edge, corner or facet). The simulated vibrational frequencies of the carbonates are found similar to the experimentally measured frequencies of some of the surface species.
In order to find stable location of the platinum cluster Pt8 on the ceria nanoparticle we checked 8 different structures with variation of the shape and location of the metal cluster. The optimized structures, initially with 4 unpaired electrons, were re-optimized with 2 and with 6 unpaired electrons. In one case the state with 4 unpaired electrons (one of which on the ceria part forming Ce(III) center) was found the most stable, while for the other structures the state with lower spin multiplicity (triplet) was found with lower energy. In the most stable structure the binding energy of platinum was calculated at 5.6 eV with five platinum atoms interacting with the ceria surface.
The calculations are performed with periodic plane-wave DFT method with PW91 exchange-correlation functional as implemented in VASP program. The kinetic energy cut-off was selected at 415 eV and a cube with dimensions of 2.00 nm each side was selected as the unit cell for the calculations. This size provides ca. 1.00 nm distance between nanoparticles in two neighboring unit cells. Due to the internal deficiency of pure DFT functionals to describe localized electrons, we applied the DFT+U approach in order to provide proper localization of the extra electron on the individual Ce(III) cations.
The investigation is supported by HPC-Europa2 program at Barcelona Supercomputer Center.
The objectives of the project were to implement two new features to the existing MPI implementation of the standard (two-level) BDDC method for solving large sparse systems arising from computations by finite element method. These new features are: (i) extension of the coarse problem solution to multiple levels and (ii) adaptive generation of the coarse problem. The code should then be tested on real-life problems from engineering.
The two-level solver has been successfully extended to handle arbitrary number of levels. This feature is important to solve very large problems using large number of subdomains on the first level. The multilevel method has been tested on benchmark problems as well as real-life engineering problems with up to six millions of unknowns and the applicability of the solver was verified also on large number of processors (512 and 1024).
A preliminary approach to adaptive selection of constraints was also implemented. It has been shown that the adaptive strategy is applicable and can dramatically reduce the final number of iterations for numerically difficult problems. However, further modifications to the algorithm seem necessary to reduce the time spent by local eigenvalue problems. This will require a careful selection of the solver for eigenproblems within the adaptive method.