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Search Results: 1 - 10 of 144478 matches for " F. Pederiva "
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Microscopically Computing Free-energy Profiles and Transition Path Time of Rare Macromolecular Transitions
P. Faccioli,F. Pederiva
Physics , 2012, DOI: 10.1103/PhysRevE.86.061916
Abstract: We introduce a rigorous method to microscopically compute the observables which characterize the thermodynamics and kinetics of rare macromolecular transitions for which it is possible to identify a priori a slow reaction coordinate. In order to sample the ensemble of statistically significant reaction pathways, we define a biased molecular dynamics (MD) in which barrier-crossing transitions are accelerated without introducing any unphysical external force. In contrast to other biased MD methods, in the present approach the systematic errors which are generated in order to accelerate the transition can be analytically calculated and therefore can be corrected for. This allows for a computationally efficient reconstruction of the free-energy profile as a function of the reaction coordinate and for the calculation of the corresponding diffusion coefficient. The transition path time can then be readily evaluated within the Dominant Reaction Pathways (DRP) approach. We illustrate and test this method by characterizing a thermally activated transition on a two-dimensional energy surface and the folding of a small protein fragment within a coarse-grained model.
Quantum Monte Carlo study of circular quantum dots in presence of Rashba interaction
A. Ambrosetti,F. Pederiva,E. Lipparini
Physics , 2010, DOI: 10.1103/PhysRevB.83.155301
Abstract: We present the numerical Quantum Monte Carlo results for the ground state energy of circular quantum dots in which Rashba spin-orbit iteraction is present. Diffusion Monte Carlo with spin propagation is applied in order to treat the spin-orbit interaction correctly, following previous work done in the fieldof the two-dimensional electron gas. Together with ground state energies, also numerical results for density and spin-density profiles are given.
Puckering Free Energy of Pyranoses Using a Combined Metadynamics-Umbrella Sampling Approach
E. Autieri,M. Sega,F. Pederiva
Physics , 2010,
Abstract: We present the results of a combined metadynamics-umbrella sampling investigation of the puckered conformers of pyranoses described using the gromos 45a4 force field. The free energy landscape of Cremer-Pople puckering coordinates has been calculated for the whole series of alpha and beta aldohexoses. We show that the 45a4 force field parameters fail in reproducing proper free energy differences between chair conformers for many of the inspected monosaccharides. In the extreme cases of galactose, mannose and allose, the experimentally non-detectable inverted chair conformers become even substantially populated. The opposite behavior is observed in the case of idose, which is the only experimentally known aldohexose that shows equilibrium between chair and inverted chair. We suggest a modification to the gromos 45a4 parameter set, which improves considerably the accordance of simulation results with theoretical and experimental estimates of puckering free energies.
Diffusion Monte Carlo study of circular quantum dots
F. Pederiva,C. J. Umrigar,E. Lipparini
Physics , 1999, DOI: 10.1103/PhysRevB.62.8120
Abstract: We present ground and excited state energies obtained from Diffusion Monte Carlo (DMC) calculations, using accurate multiconfiguration wave functions, for $N$ electrons ($N\le13$) confined to a circular quantum dot. We analyze the electron-electron pair correlation functions and compare the density and correlation energies to the predictions of local spin density approximation theory (LSDA). The DMC estimated change in electrochemical potential as function of the number of electrons in the dot is compared to that from LSDA and Hartree-Fock (HF) calculations.
Erratum: Diffusion Monte Carlo study of circular quantum dots
F. Pederiva,C. J. Umrigar,E. Lipparini
Physics , 2003, DOI: 10.1103/PhysRevB.68.089901
Abstract: Several of the energies in Tables I and II of our previous paper are incorrect. Most of the errors are due to incorrectly inputting the symmetry of some of the states, others are due to incorrectly converting or transcribing the energies. In particular, for N=4 we had a near degeneracy and a violation of Hund's first rule. The corrected result has $|L=0,S=1>$ as the ground state, as predicted by Hund's rule. Hund's first rule is satisfied for all $N$ for the confining potential used. We present corrected versions of Tables I and II.
Auxiliary Field Diffusion Monte Carlo study of the Hyperon-Nucleon interaction in $Λ$-hypernuclei
D. Lonardoni,F. Pederiva,S. Gandolfi
Physics , 2012, DOI: 10.1016/j.nuclphysa.2012.12.001
Abstract: We investigate the role of two- and three-body $\Lambda$-nucleon forces by computing the ground state of a few $\Lambda$-hypernuclei with the Auxiliary Field Diffusion Monte Carlo algorithm. Calculations have been performed for masses up to A=41, including some open-shell hypernuclei. The results show that the use of a bare hyperon-nucleon force fitted on the available scattering data yields a consistent overestimate of the $\Lambda$-separation energy $B_\Lambda$. The inclusion of a hyperon-nucleon-nucleon interaction systematically reduces $B_\Lambda$, leading to a qualitatively good agreement with experimental data over the range of masses investigated.
Effects of the two-body and three-body hyperon-nucleon interactions in Λ-hypernuclei
D. Lonardoni,S. Gandolfi,F. Pederiva
Physics , 2013, DOI: 10.1103/PhysRevC.87.041303
Abstract: Background: The calculation of the hyperon binding energy in hypernuclei is crucial to understanding the interaction between hyperons and nucleons. Purpose: We assess the relative importance of two- and three-body hyperon-nucleon force by studying the effect of the hyperon-nucleon-nucleon interaction in closed shell \Lambda-hypernuclei from A=5 to 91. Methods: The \Lambda-binding energy has been calculated using the auxiliary field diffusion Monte Carlo method for the first time, to study light and heavy hypernuclei within the same model. Results: Our results show that including a three-body component in the hyperon-nucleon interaction leads to a saturation of the \Lambda-binding energy remarkably close to the experimental data. In contrast, the two-body force alone gives an unphysical limit for the binding energy. Conclusions: The repulsive contribution of the three-body hyperon-nucleon-nucleon force is essential to reproduce, even qualitatively, the binding energy of the hypernuclei in the mass range considered.
Monte Carlo Calculation for the neutron-rich Ca isotopes
S. Gandolfi,F. Pederiva,S. a Beccara
Physics , 2006, DOI: 10.1140/epja/i2008-10536-3
Abstract: We computed ground-state energies of calcium isotopes from 42Ca to 48Ca by means of the Auxiliary Field Diffusion Monte Carlo (AFDMC) method. Calculations were performed by replacing the 40Ca core with a mean-field self consistent potential computed using Skyrme interaction. The energy of the external neutrons is calculated by projecting the ground-state from a wave function built with the single particle orbitals computed in the self consistent external potential. The shells considered were the 1F_7/2 and the 1F_5/2. The Hamiltonian employed is semi-realistic and includes tensor, spin--orbit and three--body forces. While absolute binding energies are too deep if compared with experimental data, the differences between the energies for nearly all isotopes are in very good agreement with the experimental data.
Transumbilical Laparo-Assisted Appendectomy: A Safe Operation for the Whole Spectrum of Appendicitis in Children—A Single-Centre Experience
D. Codrich,M. G. Scarpa,M. A. Lembo,F. Pederiva
Minimally Invasive Surgery , 2013, DOI: 10.1155/2013/216416
Abstract:
Quantum Monte Carlo study of the two-dimensional electron gas in presence of Rashba interaction
A. Ambrosetti,F. Pederiva,E. Lipparini,S. Gandolfi
Physics , 2009, DOI: 10.1103/PhysRevB.80.125306
Abstract: We introduce a variant to the Diffusion Monte Carlo algorithm that can be employed to study the effects of the Rashba interaction in a many electron systems. Because of the spin--orbit nature of Rashba interaction a standard algorithm cannot be applied and therefore a specific imaginary time spin dependent propagator has been developed and implemented following previous work developed in the framework of nuclear physics. We computed the ground state energy of the 2D electron gas at different densities for several values of the Rashba interaction strength as a function of "Rashba spin states" polarization. Comparison is given with analytically known Hartree-Fock results and for the system in absence of Coulomb interaction.
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