1,720,988 research outputs found
Correction: Absolute stereochemistry and preferred conformations of urate degradation intermediates from computed and experimental circular dichroism spectra
No full textEquation of motion for the solvent polarization apparent charges in the polarizable continuum model: Application to real-time TDDFT
Full text linkWhen a solute charge density is evolving in time, e.g., due to an external perturbation, the solvent reaction field also becomes time-dependent, in a nontrivial way due to the delayed response of the solvent polarization rooted in its frequency-dependent dielectric constant. In polarizable continuum models, the time-dependent reaction field is represented by time-dependent apparent surface charges. Here, we derive general expressions for such charges. In particular, for all the main flavors of PCM, including IEF-PCM, we show how the frequency-dependent dielectric function terms can be singled-out in diagonal matrices, most convenient for Fourier transforming. For spherical cavities such formulation highlights the relation with multipolar solvation models and, when applied to the related context of metal nanoparticles, discloses a direct connection with multipolar plasmons. Using the Debye dielectric function, we derive a simple equation of motion for the apparent charges, free from system history. Such an equation has been coupled to real time time-dependent density functional theory (RT-TDDFT), to simulate the time evolution of the solute density rigorously accounting for the delayed solvent reaction field. The presented method seamlessly encompasses previous nonequilibrium approaches limited to an instantaneous solute potential change (e.g., a sudden electronic excitation), does not require additional assumptions besides the basic PCM's, and is not limited to iterative inversion procedures. Numerical examples are given, showing the importance of accounting for the delayed solvent-response effects
Real-Time Description of the Electronic Dynamics for a Molecule Close to a Plasmonic Nanoparticle
No full textThe optical properties of molecules close to plasmonic nanostructures greatly differ from their isolated molecule counterparts. To theoretically investigate such systems from a quantum-chemistry perspective, one has to take into account that the plasmonic nanostructure (e.g., a metal nanoparticle-NP) is often too large to be treated atomistically. Therefore, a multiscale description, where the molecule is treated by an ab initio approach and the metal NP by a lower level description, is needed. Here we present an extension of one such multiscale model [Corni, S.; Tomasi, J. J. Chem. Phys.2001, 114, 3739], originally inspired by the polarizable continuum model, to a real-time description of the electronic dynamics of the molecule and of the NP. In particular, we adopt a time-dependent configuration interaction (TD CI) approach for the molecule, the metal NP is described as a continuous dielectric of complex shape characterized by a Drude-Lorentz dielectric function, and the molecule-NP electromagnetic coupling is treated by an equation-of-motion (EOM) extension of the quasi-static boundary element method (BEM). The model includes the effects of both the mutual molecule-NP time-dependent polarization and the modification of the probing electromagnetic field due to the plasmonic resonances of the NP. Finally, such an approach is applied to the investigation of the light absorption of a model chromophore, LiCN, in the presence of a metal-NP of complex shape
The cavity electromagnetic field within the polarizable continuum model of solvation: An application to the real-time time dependent density functional theory
No full textWe present an extension of the the cavity-field formulation for the Polarizable Continuum Model (PCM), to the Real-Time Time Dependent Density Functional Theory (RT-TDDFT). Both the length- and velocity-gauge formalisms are developed, through the approach based on effective dipole moment and momentum operators. We apply our formulation to the calculation of imaginary parts of the electric and mixed (electric-magnetic) polarizabilities, i.e. transition dipole moments and rotatory strengths for a model system, the twisted ethylene. To validate our approach we first compare the results obtained with the corresponding properties calculated within a PCM Linear-Response (LR) TDDFT formalism, and we check numerically the gauge-invariance of our formulation. Finally we also compare with the results of analytical models
Equation of motion for the solvent polarization apparent charges in the polarizable continuum model: Application to time-dependent CI
Full text linkThe dynamics of the electrons for a molecule in solution is coupled to the dynamics of its polarizable environment, i.e., the solvent. To theoretically investigate such electronic dynamics, we have recently developed equations of motion (EOM) for the apparent solvent polarization charges that generate the reaction field in the Polarizable Continuum Model (PCM) for solvation and we have coupled them to a real-time time-dependent density functional theory (RT TDDFT) description of the solute [S. Corni et al., J. Phys. Chem. A 119, 5405 (2014)]. Here we present an extension of the EOM-PCM approach to a Time-Dependent Configuration Interaction (TD CI) description of the solute dynamics, which is free from the qualitative artifacts of RT TDDFT in the adiabatic approximation. As tests of the developed approach, we investigate the solvent Debye relaxation after an electronic excitation of the solute obtained either by a π pulse of light or by assuming the idealized sudden promotion to the excited state. Moreover, we present EOM for the Onsager solvation model and we compare the results with PCM. The developed approach provides qualitatively correct real-time evolutions and is promising as a general tool to investigate the electron dynamics elicited by external electromagnetic fields for molecules in solution
First-principle-based MD description of azobenzene molecular rods
Full text linkExtensive density functional theory (DFT) calculations have been performed to develop a force field for the classical molecular dynamics (MD) simulations of various azobenzene derivatives. Besides azobenzene, we focused on a thiolated azobenzene’s molecular rod (4′-{[(1,1′-biphenyl)-4-yl]diazenyl}-(1,1′-biphenyl)-4-thiol) that has been previously demonstrated to photoisomerize from trans to cis with high yields on surfaces. The developed force field is an extension of OPLS All Atoms, and key bonding parameters are parameterized to reproduce the potential energy profiles calculated by DFT. For each of the parameterized molecule, we propose three sets of parameters: one best suited for the trans configuration, one for the cis configuration, and finally, a set able to describe both at a satisfactory degree. The quality of the derived parameters is evaluated by comparing with structural and vibrational experimental data. The developed force field opens the way to the classical MD simulations of self-assembled monolayers (SAMs) of azobenzene’s molecular rods, as well as to the quantum mechanics/molecular mechanics study of photoisomerization in SAMs
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