1,721,047 research outputs found
Tiresia: a code for molecular electronic continuum states and photoionization
Full text linkThe Tiresia program [1] provides access to numerically accurate solutions of the one-particle Schrödinger equation for highly excited states of complex polyatomic molecules, both bound and continuum, that cannot be described by conventional Quantum Chemistry approaches. It is based on an expansion of the required solution in a local multicentric basis set, with primitive functions built as products of a radial B-spline times a real spherical harmonic. In conjunction with Density Functional Theory (DFT), it has been extensively employed in a large variety of photoionization studies, also for rather large systems. Highly excited bound states as well as wavepacket propagation can also be accurately described. In fact, the flexibility of the basis essentially allows accurate solutions of linear operator equations, like Poisson or inhomogeneous perturbative equations, which are employed in the code. The program is parallelized with standard MPI-I instructions and makes extensive use of the Scalapack linear algebra library. Ancillary programs are available for the evaluation of photoionization cross sections and angular distributions from randomly to fully oriented molecules
Ultrafast charge dynamics in glycine induced by attosecond pulses
No full textThe combination of attosecond pump–probe techniques with mass spectrometry methods has recently led to the first experimental demonstration of ultrafast charge dynamics in a biomolecule, the amino acid phenylalanine [Calegari et al., Science, 2014, 346, 336]. Using an extension of the static-exchange density functional theory (DFT) method, the observed dynamics was explained as resulting from the coherent superposition of ionic states produced by the broadband attosecond pulse. Here, we have used the static-exchange DFT method to investigate charge migration induced by attosecond pulses in the glycine molecule. We show that the observed dynamics follows patterns similar to those previously found in phenylalanine, namely that charge fluctuations occur all over the molecule and that they can be explained in terms of a few typical frequencies of the system. We have checked the validity of our approach by explicitly comparing with the photoelectron spectra obtained in synchrotron radiation experiments and with the charge dynamics that follows the removal of an electron from a given molecular orbital, for which fully correlated ab initio results are available in the literature. From this comparison, we conclude that our method provides an accurate description of both the coherent superposition of cationic states generated by the attosecond pulse and its subsequent time evolution. Hence, we expect that the static-exchange DFT method should perform equally well for other medium-size and large molecules, for which the use of fully correlated ab initio methods is not possible
Strong-field control and enhancement of chiral response in bi-elliptical high-order harmonic generation: An analytical model
Full text linkThe generation of high-order harmonics in a medium of chiral molecules driven by intense bi-elliptical laser fields can lead to strong chiroptical response in a broad range of harmonic numbers and ellipticities (Ayuso et al 2018 J. Phys. B: At. Mol. Opt. Phys. 51 06LT01). Here we present a comprehensive analytical model that can describe the most relevant features arising in the high-order harmonic spectra of chiral molecules driven by strong bi-elliptical fields. Our model recovers the physical picture underlying chiral high-order harmonic generation (HHG) based on ultrafast chiral hole motion and identifies the rotationally invariant molecular pseudoscalars responsible for chiral dynamics. Using the chiral molecule propylene oxide as an example, we show that one can control and enhance the chiral response in bi-elliptical HHG by tailoring the driving field, in particular by tuning its frequency, intensity and ellipticity, exploiting a suppression mechanism of achiral background based on the linear Stark effect
Chiral dichroism in bi-elliptical high-order harmonic generation
Full text linkThe application of strong bi-elliptically polarized laser fields to the generation of high-order harmonics in organic molecules offers exceptional opportunities for chiral recognition and chiral discrimination. These fields are made by combining an elliptically polarized fundamental, typically in the infrared range, with its counter-rotating second harmonic. Here we present a theoretical study of the harmonic emission from the chiral molecule propylene oxide in bi-elliptical fields. Our calculations include, for the first time in such a complex system, accurate photorecomination matrix elements, evaluated using the static-exchange density functional theory method. We show that bi-elliptical light can induce strong chiral dichroism in the harmonic spectra of chiral molecules in a broad range of harmonic numbers and ellipticities
Theoretical study of ultrafast x-ray photoelectron diffraction from molecules undergoing photodissociation
No full textWe present a new theoretical work for the ultrafast x-ray photoelectron diffraction (UXPD) method to track photodissociation of molecules over the long range in femtosecond time scale. Our theory combines the accurate multicenter description of XPD at short to medium distances and the multiple-scattering XPD approach at larger internuclear separations. Then, the theoretical framework is applied to a demonstration of the UXPD profiles from halogen diatomics undergoing photodissociation. The computational results indicate that such a combination of the two theoretical approaches sufficiently works to seamlessly track the conformational evolution during photodissociation. The present study provides information on dissociation kinetics of neutral diatomic molecules available with the UXPD method and is a step towards an approach applied to general photoelimination processe
B-Spline Solution of the Two-Center Dirac Equation in the Electronic Continuum for Relativistic Molecular Photoionization
No full textIn this work, the two-center Dirac equation is solved numerically using an extension of an adapted B-spline basis set method previously implemented in relativistic atomic calculations (Fischer, C. F.; Zatsarinny, O. Comput. Phys. Commun. 2009, 180, 879). The robustness of the chosen numerical method, which avoids the appearance of spurious states common in other approaches, allows us to investigate molecular photoionization within a relativistic framework by simply adapting those methods already available in the nonrelativistic case (Brosolo, M.; Decleva, P. Chem. Phys. 1992, 159, 185; Brosolo, M.; Decleva, P.; Lisini, A. Mol. Opt. Phys. 1992, 25, 3345). First, light diatomic molecules (i.e., H2+ and HeH2+) are investigated with the purpose of testing the validity and efficiency of the method. Then, a series of one-electron molecular hydrides (i.e., HF9+, HCl17+ and HI53+) is explored by computing the total photoionization cross sections, asymmetry β-parameters and partial phase shifts. The present methodology can be easily extended to treat N-electron molecules following previous approaches in nonrelativistic calculations (Plesiat, E.; Decleva, P.; Martin, F. Phys. Chem. Chem. Phys. 2012, 14, 10853). The inclusion of a second photon can be also accomplished just like in atomic investigations aiming at reproducing pump-probe experiments capable to extract the photoionization time-delays (Vinbladh, J.; Dahlstrom, J. M.; Lindroth, E. Phys. Rev A 2019, 100, 043424; Vinblach, J.; Dahlstrom, J. M.; Lindroth, E. Atoms 2022, 10, 80)
Photoionization of furan from the ground and excited electronic states
No full textHere we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy
Role of electron-nuclear coupled dynamics on charge migration induced by attosecond pulses in glycine
No full textWe present a theoretical study of charge dynamics initiated by an attosecond XUV pulse in the glycine molecule, which consists in delocalized charge fluctuations all over the molecular skeleton. For this, we have explicitly used the actual electron wave packet created by such a broadband pulse. We show that, for the chosen pulse, charge dynamics in glycine is barely affected by nuclear motion or non adiabatic effects during the first 8 fs, and that the initial electronic coherences do not dissipate during the first 20 fs. In contrast, small variations in the initial nuclear positions, compatible with the geometries expected in the Franck-Condon region, lead to noticeable changes in this dynamics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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