9,212 research outputs found
Toward spectroscopic accuracy for open-shell systems: X2AB radicals as test cases
No full textThe structures, force fields and electro-magnetic properties of small molecules represent invaluable benchmarks for the most refined quantum mechanical (QM) approaches and an ideal playground where the accuracy of experimental and computational approaches rivals and synergically increases. At the same time, development and validation of the more approximate QM approaches, which are unavoidable for large systems, strongly benefit from the rich and variegate information issuing from sophisticate benchmark computations for the widest possible range of physico-chemical properties. On these grounds, very reliable extrapolation procedures have been developed and validated, which, however, mostly refer to closed-shell systems. The situation is more involved for open-shell systems due to both increased technical difficulties and to the paramount relevance of EPR spectroscopy, which requires, in turn, reliable computations of specific properties (especially isotropic hyperfine couplings) with peculiar method/basis set requirements [1]. At the same time, direct structural information are seldom available and assignments of vibrational frequencies are often not straightforward [2].
This prompted us to start a comprehensive research program on prototypical small organic X2AB radicals (with X=halogen atom, A=B,C,N and B=N,O) with the aim of extending the data base of highly accurate QM results to the structures, force fields and magnetic properties. All of these have been computed by the coupled cluster ansatz using a hierarchic series of basis sets and, in some cases, extrapolation procedures to reach the complete basis set limit. Methods rooted into the density functional theory have been used to estimate vibrational and environmental effects. The remarkable agreement with available experimental data confirms the reliability of the computational approach followed and suggests that our predictions for missing information should be highly reliable.
References
1. Improta R., Barone V., Chem. Rev. (Washington, D. C.) 2004, 104, 1231; Al Derzi A.R., Fau S., Bartlett R., J. Phys. Chem. A 2006, 110, 4473; Barone V., Cimino P., Stendardo E., J. Comp. Theor. Chem. 2008, 4, 751.
2. Sattelmeyer K.W., Schaefer III H.F., J. Chem. Phys. 2002, 117, 7914; Barone V., Carbonniere P., Pouchan C., J. Chem. Phys. 2005, 122, 224308
Traduzioni sotto il 41° parallelo Curatela
No full textIl volume raccoglie le traduzioni di testi in prosa (racconti, saggi, capitoli di romanzi) a cura degli studenti del corso di Lingua inglese V del corso di laurea in Lingue e Letterature Moderne coordinati da Linda Barone
Thermal activation and macroscopic quantum tunneling in Josephson junctions
No full textIn the present work are collected some recent results obtained concerning the thermal fluctuations and macroscopic quantum tunneling in Josphson systems mostly in connection with their effect on their current-voltage I-V characteristics of a tunnel junction. This study considers both underdamped and overdamped situations looking for proper expressions for the lifetime of both ''locked'' and ''running'' states corresponding to zero and finite voltage current-carrying states of the junction. In this way the authors investigate some aspects of the influence of noise on the I-V curves of Josephson junctions. Using the first-time passage technique developed by Stratonovich expressions which extend the classical Kramers results are obtained. In conclusion, considered is the non-stationary case to explain the presence of hysteresis and sharp transitions in the I-V curves in presence of thermal noise. It is easy to understand how the previous considerations on the activation processes also leads to the stationary case. If during the observations the average on times is larger than both tau-right arrow and tau-left arrow the process is stationary and single-value rounded I-V curves are observe
Linda Barone, Bruna Di Sabato, Monica Manzolillo. <i>L’educazione linguistica e letteraria</i>
No full textRecensione di Barone, L.; Di Sabato, B.; Manzolillo, M. (2021). L’educazione linguistica e letteraria. Un approccio integrato. Novara: UTET, 330 pp.</jats:p
The Persico equation for minimum uncertainty states
No full textWe present an important and forgotten result of fundamental quantum mechanics obtained in 1930 by Enrico Persico, consisting of an eigenvalue equation for minimum uncertainty states
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