41 research outputs found
25 + 65: Un any d'efemèrides per a la química teòrica de Catalunya
La química teòrica de Catalunya va commemorar durant el 2009 dues efemèrides importants: la XXV Reunió Anual i el seixanta-cinquè aniversari del professor Santiago Olivella.The theoretical chemistry community in Catalonia celebrated two important events in 2009: the XXVth Anual Meeting
and the 65th birthday of Professor Santiago Olivella
Revisiting the early days of theoretical and computational chemistry in Catalonia
En aquest article recorrem els primers temps de la química teòrica i computacional de Catalunya, en reconeixença dels pioners que van possibilitar que aquesta branca de la química en sigui avui un dels motors. La consolidació i el reconeixement que ha assolit es deuen a les recerques específiques que han permès aportar claus d’interpretació i de predicció en diferents camps de la química, dels materials i de la bioquímica, però també, a la potent xarxa col·lectiva que va trobar les vies per a fer visible el paper tan important d’aquesta especialitat.In this paper we retrace the early days of theoretical and computational chemistry in Catalonia, in recognition of the pioneers who made it possible for this research field to be one of the driving forces of chemistry today. Its consolidation and recognition has been due to the specific research providing keys for interpretation and prediction in different fields of chemistry, materials science and biochemistry, as well as to the strong collective network that found ways to enhance the prominence of theoretical and computational chemistry’s important role
Analysis of the magnetic coupling in binuclear complexes. II. Derivation of valence effective Hamiltonians from ab initio Cl and DFT calculations
Most interpretations of the magnetic coupling J between two unpaired electrons rest upon simple
valence models that involve essentially the ferromagnetic direct exchange contribution, Kab , and
the antiferromagnetic effect of the delocalization resulting from the interaction between neutral and
ionic determinants, tab , whose energy difference is U. Ab initio valence-only calculations give very
poor estimates of J, whatever the definition of the magnetic orbitals, and large CI expansions are
required to evaluate it properly. It is, however, possible to define valence effective Hamiltonians
from the knowledge of the eigenenergies and the eigenvectors of these accurate CI calculations.
When applied to four different complexes, this strategy shows that spin polarization may change the
sign of the direct exchange interaction, Kab , and that dynamical correlation results in a dramatic
reduction of the effective repulsion U. The present article also shows how Kab , tab , and U effective
parameters can be extracted from density functional theory ~DFT! calculations and that the typical
overestimation of J in DFT can be attributed to an excessive lowering of the effective on-site
repulsio
Electronic structure of Ca Cu2 O3: Spin ladder versus one-dimensional spin chain
Quantum chemical calculations on embedded cluster models have been performed to extract accurate estimates
of the magnetic coupling J and hopping parameters t of CaCu2O3. It is shown that this copper oxide
compound is best described as a quasi-one-dimensional spin chain with weak interchain interactions within and
between the Cu2O3 planes. This magnetic structure is not reflected in the hopping parameters, since we find a
large interplane hopping. Hence, the use of the simple second-order expression that relates J, t, and the on-site
repulsion U sJ=−4t2 /Ud is not justified in all case
Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited
In magnetic coordination compounds and solids the magnetic orbitals are essentially located on
metallic centers but present some delocalization tails on adjacent ligands. Mean field variational
calculations optimize this mixing and validate a single band modelization of the intersite magnetic
exchange. In this approach, due to the Brillouin’s theorem, the ligand to metal charge transfer
LMCT excitations play a minor role. On the other hand the extensive configuration interaction
calculations show that the determinants obtained by a single excitation on the top of the LMCT
configurations bring an important antiferromagnetic contribution to the magnetic coupling.
Perturbative and truncated variational calculations show that contrary to the interpretation given in
a previous article C. J. Calzado et al., J. Chem. Phys. 116, 2728 2002 the contribution of these
determinants to the magnetic coupling constant is not a second-order one. An analytic development
enables one to establish that they contribute at higher order as a correlation induced increase in the
LMCT components of the wave function, i.e., of the mixing between the ligand and the magnetic
orbitals. This larger delocalization of the magnetic orbitals results in an increase in both the ferroand
antiferromagnetic contributions to the coupling constan
Four-spin cyclic exchange in spin ladder cuprates
The four-spin cyclic exchange term Jring of three spin-ladder cuprates (SrCu2O3, Sr2Cu3O5, and CaCu2O3) has been calculated from ab initio quantum chemistry calculations. For the first two compounds, a non-negligible cyclic exchange is found, aproximately 20% of the magnetic coupling across the rungs, J⊥, and always larger than the value obtained for two-dimensional La2CuO4 system. In the case of CaCu2O3, the Jring value is quite small, due to the folding of the Cu-O-Cu rung angle, but the Jring/J⊥ ratio is also 0.2 as in the two other system
Analysis of the magnetic coupling in binuclear complexes. I. Physics of the coupling
Accurate estimates of the magnetic coupling in binuclear complexes can be obtained from ab initio
configuration interaction ~CI! calculations using the difference dedicated CI technique. The present
paper shows that the same technique also provides a way to analyze the various physical
contributions to the coupling and performs numerical analysis of their respective roles on four
binuclear complexes of Cu (d9) ions. The bare valence-only description ~including direct and
kinetic exchange! does not result in meaningful values. The spin-polarization phenomenon cannot
be neglected, its sign and amplitude depend on the system. The two leading dynamical correlation
effects have an antiferromagnetic character. The first one goes through the dynamical polarization of
the environment in the ionic valence bond forms ~i.e., the M1¯M2 structures!. The second one is
due to the double excitations involving simultaneously single excitations between the bridging
ligand and the magnetic orbitals and single excitations of the environment. This dispersive effect
results in an increase of the effective hopping integral between the magnetic orbitals. Moreover, it
is demonstrated to be responsible for the previously observed larger metal-ligand delocalization
occurring in natural orbitals with respect to the Hartree–Fock one
Effectiveness, cost-utility, and benefits of a multicomponent therapy to improve the quality of life of patients with fibromyalgia in primary care: A mixed methods study protocol
Introduction: Fibromyalgia (FM) is a chronic condition characterized by chronic pain, fatigue and loss of function which significantly impairs quality of life. Although treatment of FM remains disputed, some studies point at the efficacy of interdisciplinary therapy. This study aims to analyze the effectiveness, cost-utility and benefits of a multicomponent therapy on quality of life (main variable), functional impact, mood and pain in people suffering from FM that attend primary care centers (PCCs) of the Catalan Institute of Health (ICS). Methods and analysis: A 2-phase, mixed methods study has been designed following Medical Research Council guidance. Phase 1: Pragmatic randomized clinical trial with patients diagnosed with FM that attend one of the 11 PCCs of the ICS Gerència Territorial Terres de l'Ebre. We estimate a total sample of 336 patients. The control group will receive usual clinical care, while the multicomponent therapy group (MT group) will receive usual clinical care plus group therapy (consisting of health education, exercise and cognitive-behavioural therapy) during 12 weeks in 2-hourly weekly sessions. Analysis: the standardized mean response and the standardized effect size will be assessed at 3, 9, and 15 months after the beginning of the study using multiple linear regression models. Utility measurements will be used for the economic analysis. Phase 2: Qualitative socio constructivist study to evaluate the intervention according to the results obtained and the opinions and experiences of participants (patients and professionals). We will use theoretical sampling, with 2 discussion groups of participants in the multicomponent therapy and 2 discussion groups of professionals of different PCCs. A thematic content analysis will be carried out. Ethics and dissemination: This study protocol has been approved by the Clinical Research Ethics Committee of the Fundació Institut Universitari per a la recerca a l'Atenció Primària de Salut Jordi Gol i Gurina (code P18/068). Articles will be published in international, peer-reviewed scientific journals
Effectiveness, cost-utility, and benefits of a multicomponent therapy to improve the quality of life of patients with fibromyalgia in primary care : a mixed methods study protocol
Introduction:Fibromyalgia (FM) is a chronic condition characterized by chronic pain, fatigue and loss of function which significantly impairs quality of life. Although treatment of FM remains disputed, some studies point at the efficacy of interdisciplinary therapy. This study aims to analyze the effectiveness, cost-utility and benefits of a multicomponent therapy on quality of life (main variable), functional impact, mood and pain in people suffering from FM that attend primary care centers (PCCs) of the Catalan Institute of Health (ICS).Methods and analysis:A 2-phase, mixed methods study has been designed following Medical Research Council guidance. Phase 1: Pragmatic randomized clinical trial with patients diagnosed with FM that attend one of the 11 PCCs of the ICS Gerència Territorial Terres de l'Ebre. We estimate a total sample of 336 patients. The control group will receive usual clinical care, while the multicomponent therapy group (MT group) will receive usual clinical care plus group therapy (consisting of health education, exercise and cognitive-behavioural therapy) during 12 weeks in 2-hourly weekly sessions. Analysis: the standardized mean response and the standardized effect size will be assessed at 3, 9, and 15 months after the beginning of the study using multiple linear regression models. Utility measurements will be used for the economic analysis. Phase 2: Qualitative socio constructivist study to evaluate the intervention according to the results obtained and the opinions and experiences of participants (patients and professionals). We will use theoretical sampling, with 2 discussion groups of participants in the multicomponent therapy and 2 discussion groups of professionals of different PCCs. A thematic content analysis will be carried out.Ethics and dissemination:This study protocol has been approved by the Clinical Research Ethics Committee of the Fundació Institut Universitari per a la recerca a l'Atenció Primària de Salut Jordi Gol i Gurina (code P18/068). Articles will be published in international, peer-reviewed scientific journals.Trial registration:Clinical-Trials.gov: NCT04049006
25 + 65: Un any d'efemèrides per a la química teòrica de Catalunya
La química teòrica de Catalunya va commemorar durant el 2009 dues efemèrides importants: la XXV Reunió Anual i el seixanta-cinquè aniversari del professor Santiago Olivella.The theoretical chemistry community in Catalonia celebrated two important events in 2009: the XXVth Anual Meeting
and the 65th birthday of Professor Santiago Olivella