1,721,006 research outputs found
Bose-Fermi mixtures with pairing
Full text linkI will review recent work by us on the properties of Bose-Fermi mixtures with a tunable pairing interaction
between bosons and fermions. A many-body diagrammatic approach, able to describe the condensed phase of
a Bose-Fermi mixture from weak to strong boson-fermion couplings, will be presented [1]. This approach will
be validated by comparing it with previous [2] and new dedicated fixed-node diffusion Monte Carlo
calculations. By using both methods, a universal behavior of the condensate fraction and bosonic momentum
distribution with respect to the boson concentration is found in an extended range of boson-fermion couplings
and concentrations. For vanishing boson density, the bosonic condensate fraction reduces to the quasiparticle
weight Z of the Fermi polaron studied in the context of polarized Fermi gases, unifying in this way two
apparently unrelated quantities. Finally, I will discuss an interesting effect occurring in the molecular limit of
the boson- fermion coupling, where the condensation is completely suppressed [3]. This phenomenon is an
indirect effect on bosons of the Pauli exclusion principle acting on fermions, and is the counterpart in BoseFermi
mixtures of the so called “Sarma phase” discussed for polarized Fermi gases.
[1] A. Guidini, G. Bertaina, D. Galli, and P. Pieri, arXiv:1412.2542.
[2] G. Bertaina, E. Fratini, S. Giorgini, and P. Pieri, Phys. Rev. Lett. 110, 115303 (2013).
[3] A. Guidini, G. Bertaina, E. Fratini, and P. Pieri, Phys. Rev. A 89, 023634 (2014)
Quantum nuclear densities from semiclassical on-the-fly molecular dynamics
No full textSemiclassical molecular dynamics is a rigorous approximation to quantum dynamics obtained from the exact quantum propagator expressed as Feynman’s path integral.[1] Recently, our group has introduced the Multiple Coherent Semiclassical Initial Value Representation (MC SCIVR) technique to reduce the number of classical trajectories required to converge vibrational spectra calculations from thousands to just a handful.[2-4] MC SCIVR has been applied successfully to several medium and large-size molecular systems,[4-10] including fluxional and condensed phase ones.[11-13] In addition to the accurate anharmonic vibrational eigenvalue calculations, MC SCIVR yields vibrational eigenfunctions for both the ground and excited vibrational states.[14] In this talk, I will survey how we obtain the quantum anharmonic vibrational eigenfunctions from ab-initio on-the-fly trajectory simulations and how we extract the quantum nuclear densities and the geometry parameters probability distributions.[15,16] This information allows us to assign each peak in vibrational spectra, going beyond the usual harmonic normal-mode analysis. Our technique quantitatively determines how normal modes involving different functional groups cooperate to originate the spectroscopic
signal. Furthermore, it allows for the visualization of the nuclear vibrations in a purely quantum picture, letting us both directly observe and quantify the effects of the full potential energy surface anharmonicity on the molecular structure. In particular, I will illustrate applications to the protonated glycine to reveal quantum mechanical and anharmonic vibrational features. The method will allow for a better rationalization of experimental spectroscopy.
[1] W.H. Miller, J. Phys. Chem. A 2001, 105, 2942.
[2] M. Ceotto, S. Atahan, S. Shim, G.F. Tantardini, A. Aspuru-Guzik, Phys. Chem. Chem. Phys. 2009, 11, 3861.
[3] M. Ceotto, S. Atahan, G.F. Tantardini, A. Aspuru-Guzik J. Chem. Phys. 2009, 130, 234113.
[4] R. Conte, M. Ceotto, In Quantum Chemistry and Dynamics of Excited States: Methods and Applications (eds L. González and R. Lindh) 2020.
[5] M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett. 2017, 119, 010401.
[6] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2017, 13, 2378.
[7] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 014307.
[8] F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, Chem. Sci. 2018, 9, 7894.
[9] F. Gabas, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 150, 224107.
[10] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2020, 16, 3476.
[11] G. Bertaina, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 151, 114307.
[12] A. Rognoni, R. Conte, M. Ceotto, Chem. Sci., 2021, 12, 2060.
[13] M. Cazzaniga, M. Micciarelli, F. Moriggi, A. Mahmoud, F. Gabas, and M. Ceotto, J. Chem. Phys. 2020, 152, 104104.
[14] M. Micciarelli, R. Conte, J. Suarez, M. Ceotto, J. Chem. Phys. 2018 149, 064115.
[15] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, Nat. Commun 2020, 11, 1.
[16] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, J. Chem. Phys., 2020, 153, 214117
Quantum nuclear densities from semiclassical on-the-fly molecular dynamics
No full textSemiclassical molecular dynamics is a rigorous approximation to quantum dynamics obtained from the exact quantum propagator expressed as Feynman’s path integral.[1] Recently, our group has introduced the Multiple Coherent Semiclassical Initial Value Representation (MC SCIVR) technique to reduce the number of classical trajectories required to converge vibrational spectra calculations from thousands to just a handful.[2-4] MC SCIVR has been applied successfully to several medium- and large-size molecular systems,[4-10] including fluxional and condensed phase ones.[11-13] In addition to the accurate anharmonic vibrational eigenvalue calculations, MC SCIVR yields vibrational eigenfunctions for both the ground and excited vibrational states.[14] In this talk, I will survey how we obtain the quantum anharmonic vibrational eigenfunctions from ab-initio on-the-fly trajectory simulations and how we extract the quantum nuclear densities and the geometry parameters probability distributions.[15,16] This information allows us to assign each peak in vibrational spectra, going beyond the usual harmonic normal-mode analysis. Our technique quantitatively determines how normal modes involving different functional groups cooperate to originate the spectroscopic signal. Furthermore, it allows for the visualization of the nuclear vibrations in a purely quantum picture, letting us both directly observe and quantify the effects of the full potential energy surface anharmonicity on the molecular structure. In particular, I will illustrate applications to the protonated glycine to reveal quantum mechanical and anharmonic vibrational features. The method will allow for a better rationalization of experimental spectroscopy.
[1] W.H. Miller, J. Phys. Chem. A 2001, 105, 2942.
[2] M. Ceotto, S. Atahan, S. Shim, G.F. Tantardini, A. Aspuru-Guzik, Phys. Chem. Chem. Phys. 2009, 11, 3861.
[3] M. Ceotto, S. Atahan, G.F. Tantardini, A. Aspuru-Guzik J. Chem. Phys. 2009, 130, 234113.
[4] R. Conte, M. Ceotto, In Quantum Chemistry and Dynamics of Excited States: Methods and Applications (eds L. González and R. Lindh) 2020.
[5] M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett. 2017, 119, 010401.
[6] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2017, 13, 2378.
[7] G. Di Liberto, R. Conte, M. Ceotto, J. Chem. Phys. 2018, 148, 014307.
[8] F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, Chem. Sci. 2018, 9, 7894.
[9] F. Gabas, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 150, 224107.
[10] F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput. 2020, 16, 3476.
[11] G. Bertaina, G. Di Liberto, M. Ceotto, J. Chem. Phys. 2019, 151, 114307.
[12] A. Rognoni, R. Conte, M. Ceotto, Chem. Sci., 2021, 12, 2060.
[13] M. Cazzaniga, M. Micciarelli, F. Moriggi, A. Mahmoud, F. Gabas, and M. Ceotto, J. Chem. Phys. 2020, 152, 104104.
[14] M. Micciarelli, R. Conte, J. Suarez, M. Ceotto, J. Chem. Phys. 2018 149, 064115.
[15] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, Nat. Commun 2020, 11, 1.
[16] C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, J. Chem. Phys., 2020, 153, 214117
Two-dimensional attractive fermi gas : balanced and highly polarized regimes at zero temperature
Full text linkWe study a two dimensional two species Fermi gas with attractive short-range interactions at zero
temperature, both in the unpolarized regime, which shows a BCS-BEC crossover type of superfluid
ground state, and in the highly polarized regime, corresponding to an impurity immersed in a Fermi
sea, which exhibits a transition from a polaronic to a molecular ground state. We use Diffusion Monte Carlo with Fixed Node approximation in order to calculate the energy per particle and extract the effective interactions among composite particles in the strongly interacting regime, where beyond mean field effects are crucial. In the impurity regime we calculate the evolution of the quasiparticle weight in the attractive polaronic branch as a function of the coupling. We also discuss the relevance of these results to ongoing experiments
Quantum nuclear densities from semiclassical on-the-fly molecular dynamics
No full textSemiclassical molecular dynamics is a rigorous approximation to quantum dynamics obtained from the exact quantum propagator expressed as Feynman’s path integral.[1] Recently, our group has introduced the Multiple Coherent Semiclassical Initial Value Representation (MC SCIVR) technique to reduce the number of classical trajectories required to converge vibrational spectra calculations from thousands to just a handful.[2-4] MC SCIVR has been applied successfully to several medium-and large-size molecular systems,[4-10] including fluxional and condensed phase ones.[11-13] In addition to the accurate anharmonic vibrational eigenvalue calculations, MC SCIVR yields vibrational eigenfunctions for both the ground and excited vibrational states.[14] In this work, we obtain the quantum anharmonic vibrational eigenfunctions from ab-initio on-the-fly trajectory simulations, and we extract the quantum nuclear densities and the geometry parameters probability distributions.[15,16] This information allows us to assign each peak in vibrational spectra, going beyond the usual harmonic normal-mode analysis. Our technique quantitatively determines how normal modes involving different functional groups cooperate to originate the spectroscopic signal. Furthermore, it allows for the visualization of the nuclear vibrations in a purely quantum picture, letting us directly observe and quantify the effects of the full potential energy surface anharmonicity on the molecular structure. In particular, for the protonated glycine molecule, our calculations reveal quantum mechanical and anharmonic vibrational features. The method will allow for a better rationalization of experimental spectroscopy.
References
[1]W. Miller, J. Phys. Chem. A, 105, 2942-2955 (2001)
[2]M. Ceotto, S. Atahan, S. Shim, G. Tantardini, A. Aspuru-Guzik, Phys. Chem. Chem. Phys., 11, 3861 (2009)
[3]M. Ceotto, S. Atahan, G. Tantardini, A. Aspuru-Guzik, The Journal of Chemical Physics, 130, 234113 (2009)
[4]R. Conte, M. Ceotto, Semiclassical Molecular Dynamics for Spectroscopic Calculations, 2020
[5]M. Ceotto, G. Di Liberto, R. Conte, Phys. Rev. Lett., 119, 010401 (2017)
[6]F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput., 13, 2378-2388 (2017)
[7]G. Di Liberto, R. Conte, M. Ceotto, The Journal of Chemical Physics, 148, 014307 (2018)
[8]F. Gabas, G. Di Liberto, R. Conte, M. Ceotto, Chem. Sci., 9, 7894-7901 (2018)
[9]F. Gabas, G. Di Liberto, M. Ceotto, J. Chem. Phys., 150, 224107 (2019)
[10]F. Gabas, R. Conte, M. Ceotto, J. Chem. Theory Comput., 16, 3476-3485 (2020)
[11]G. Bertaina, G. Di Liberto, M. Ceotto, J. Chem. Phys., 151, 114307 (2019)
[12]A. Rognoni, R. Conte, M. Ceotto, Chem. Sci., 12, 2060-2064 (2021)
[13]M. Cazzaniga, M. Micciarelli, F. Moriggi, A. Mahmoud, F. Gabas, M. Ceotto, J. Chem. Phys., 152, 104104 (2020)
[14]M. Micciarelli, R. Conte, J. Suarez, M. Ceotto, The Journal of Chemical Physics, 149, 064115 (2018)
[15]C. Aieta, M. Micciarelli, G. Bertaina, M. Ceotto, Nat. Commun., 11, 4348 (2020)
[16]C. Aieta, G. Bertaina, M. Micciarelli, M. Ceotto, J. Chem. Phys., 153, 214117 (2020
BCS-BEC crossover in two dimensions: a Quantum Monte Carlo study
Full text linkWe investigate the crossover from Bardeen-Cooper-Schrieffer (BCS) superfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi gas at T = 0 using the fixed-node diffusion Monte Carlo method. We calculate the equation of state and the gap parameter as a function of the interaction strength, observing large deviations compared to mean-field predictions. In the BEC regime our results show the important role of dimer-dimer and atom-dimer interaction effects that are completely neglected in the mean-field picture. We also consider the highly polarized gas and the competition between a polaronic and a molecular picture.IT
Quantum Monte Carlo study of a resonant Bose-Fermi mixture
Full text linkWe study resonant Bose-Fermi mixtures at zero temperature, with different relative concentrations
of the bosons. We use for the first time a Quantum Monte Carlo method with Fixed-Node approxima-
tion, to explore the system from the weak to the strong coupling limit. A repulsive interaction among
bosons is introduced to provide stability to the bosonic component. Beyond the unitarity limit, the res-
onant attractive interaction supports a bound fermionic dimer. At the many-body level, increasing the
boson-fermion coupling the system undergoes a quantum phase transition from a state with condensed bosons immersed in a Fermi sea, to a normal Fermi-Fermi mixture of the composite fermions and the bare fermions in excess. We obtain the equation of state and we characterize the momentum distributions both in the weakly and in the strongly interacting limits. We compare Quantum Monte Carlo results to T-matrix calculations, finding interesting signatures of the different many-body ground states
Two-dimensional short-range interacting attractive and repulsive Fermi gases at zero temperature
Full text linkWe study a two-dimensional two-component Fermi gas with attractive or repulsive short-range interactions at zero temperature. We use Diffusion Monte Carlo with Fixed Node approximation in order to calculate the energy per particle and the opposite spin pair distribution functions. We show the relevance of beyond mean field effects and verify the consistency of our approach by using Tan’s Contact relations.LTP
Density profiles of polarized Fermi gases confined in harmonic traps
Full text linkOn the basis of the phase diagram of the uniform system, we calculate the density profiles of a trapped polarized Fermi gas at zero temperature using the local density approximation. By varying the overall polarization and the interaction strength, we analyze the appearance of a discontinuity in the profile, signaling a first-order phase transition from a superfluid inner core to a normal outer shell. The local population imbalance between the two components and the size of the various regions of the cloud corresponding to different phases are also discussed. The calculated profiles are quantitatively compared with the ones recently measured by Shin [Phys. Rev. Lett. 101, 070404 (2008)]
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