RESUMEN
Photoinduced nonadiabatic processes play a crucial role in a wide range of disciplines, from fundamental steps in biology to modern applications in advanced materials science. A theoretical understanding of these processes is highly desirable, and trajectory surface hopping (TSH) has proven to be a well-suited framework for a wide range of systems. In this work, we present a comprehensive comparison between two TSH algorithms, the conventional Tully's fewest switches surface hopping (FSSH) scheme and the Landau-Zener surface hopping (LZSH), to study the photoinduced ring-opening of 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene at the spin-flip time-dependent density functional theory (SF-TDDFT) level of theory. Additionally, we compare our results with a literature study at the extended multistate complete active space second-order perturbation theory method (XMS-CASPT2) level of theory. Our results show that the average population and lifetimes estimated with LZSH using SF-TDDFT are closer to the literature (using multireference methods) than those estimated with FSSH using SF-TDDFT. The latter speaks in favor of applying LZSH in combination with the SF-TDDFT method to study larger and more complex systems such as molecular photoswitches where the CHD molecule acts as a backbone. In addition, we present an implementation of Tully's FSSH algorithm as an extension to the PySurf software package.
RESUMEN
Dithienylethene (DTE) molecular photoswitches have shown to be excellent candidates in the design of efficient optoelectronic devices, due to their high photoisomerization quantum yield (QY), for which symmetry is suggested to play a crucial role. Here, we present a theoretical study on the photochemistry of a non-symmetric dithienylethene photoswitch, with a special emphasis on the effect of asymmetric substitution on the photocyclization and photoreversion mechanisms. We used the Spin-Flip Time Dependent Density Functional Theory (SF-TDDFT) method to locate and characterize the main structures (conical intersections and minima) of the ground state and the first two excited states, S1 and S2, along the ring-opening/closure reaction coordinate of the photocyclization and photoreversion processes, and to identify the important coordinates governing the radiationless decay pathways. Our results suggest that while the main features that characterize the photoisomerization of symmetric DTEs are also present for the photoisomerization of the non-symmetric DTE, the lower energy barrier on S1 along the cycloreversion reaction speaks in favor of a more efficient and therefore a higher cycloreversion QY for the non-symmetric DTEs, making them a better candidate for molecular optoelectronic devices than their symmetric counterparts.
RESUMEN
Background: the computer program WHONET generates a common database to analyze local or general antimicrobial resistance of bacteria. A surveillance of agents causing urinary tract infections in Chile has been performed using this program. Aim: to report the results after 12 months of urinary tract infection agent surveillance. Material and methods: since november, 1997, a surveillance of in vitro antimicrobial resistance, using agar diffusion techniques, has been performed in 20 to 40 bacterial strains per month, isolated from 11 hospitals in the country. Results have been analyzed using WHONET program. Results: in first 12 months, 3144 strains, 1625 coming from outpatients, have been studied. Seventy four percent of isolated strains were E. coli, 19 percent were other enterobacteria, 4.1 percent were non fermenting bacilli and 2.1 percent were Gram (+) cocci. Sixty five percent of E coli strains were resistant to ampicillin, 11 percent to cefazolin, 2.5 percent to cefuroxime, 19 percent to ceftriaxone, 9 percent to ceftazidime, 4.2 percent to gentamicin 1.3 percent to amikacin, 5.6 percent to ciprofloxacin, 8.4 percent to grepafloxacin, 4.3 percent to nitrofurantoin and 43 percent to trimeproprim/sulphamethoxazole. Eighty two percent of other enterobacteria strains were resistant to ampicillin, 45.5 percent to cefazolin, 33.5 percent to cefuroxime, 26.6 percent to ceftriaxone, 21.5 percent to ceftazidime, 30.3 percent to gentamicin 17.2 percent to amikacin, 21 percent to ciprofloxacin, 16.3 percent to grepafloxacin, 48.2 percent to nitrofurantoin and 44.6 percent to trimeproprim/sulphamethoxazole. There were differences in betalactamic resistance among hospitals. Conclusions: noteworthy is the high resistance rates to third generation cephalosporins, evidenced when the new cutoff values for E coli and klebsiella spp are used. This national surveillance provides updated information on antimicrobial resistance of agents causing urinary tract infections