Department of Physical Chemistry (2012 - Present)
chemistry
, Tarbiat Modares University,
chemistry
, University of Tehran, Iran
pure chemistry
, University of Esfahan, Iran
Mohsen Vafaee PhD of Physical Chemistry, Tarbiat Modares University, October 2004
Exploring highly active, stable, and inexpensive electrocatalysts for the oxygen reduction reaction (ORR) is pivotal in developing high-performance energy conversion devices. Moreover, the production of catalysts containing transition metals with the appropriate nitrogen doping level is a potential approach to increase ORR catalytic efficiency, especially under acidic conditions. In this study, a hierarchical graphitic porous carbon-containing Fe and N was obtained via pyrolysis of a bimetal MOF (Fe/ZIF-8) composited with pyrrole. Further experimental and theoretical results confirmed that the synergistic effects between Fe-based nanoparticles and N-doping in the networks are likely form one of the main reasons for better ORR performance. U
In this work, by density functional theory (DFT) calculations, sp–sp2-hybridized boron-doped graphdiyne (BGDY) nanosheets have been investigated as an anode material for sodium storage. The density of states (DOS) and band structure plots show that substituting a boron atom with a carbon atom in an 18-atom unit cell converts the semiconductor pristine graphdiyne (GDY) to metallic BGDY. Also, our calculations indicate that, due to the presence of boron atoms, the adsorption energy of BGDY is more than that of GDY. The diffusion energy barrier calculations show that the boron atom in BGDY creates a more suitable path with a low energy barrier for sodium movement. This parameter is important in the rate of charge/discharge process. On the ot
A new phenomenon, i.e. the improvement of the adsorption energy and the diffusion of Li ion in a phosphorene monolayer under the effect of perpendicular external electric field (EEF) was studied using M06-2X/6-31G(d,p) density functional theory (DFT) framework, and also outcomes were compared with the results obtained by using of graphene. Potential energy surface (PES) scanning and analysis of origin-dependency of charged molecular systems’ energy, were used to obtain intrinsic binding energy of the charged molecular compounds within the external electric field. Our calculations revealed that, increasing the strength of field from −0.02 to 0.032 a u, caused the adsorption energies of the Li ion in the phosphorene monolayer to be incr
In this report, a novel methodology based on the static coherent states approach is introduced with the capability of calculating various strong-field laser-induced nonlinearities in full dimensional single-electron molecular systems; an emphasis is made on the high-order harmonic generation. To evaluate the functionality of this approach, we present a case study of the Hydrogen molecular ion\ih interacting with a few-cycle linearly polarized optical laser with trapezoidal waveform. We detected that the accuracy of the obtained harmonics is considerably enhanced by averaging the expectation value of the acceleration of the single electron over a set of identical random simulations. Subsequently, the presented approach demands a significantl
We discuss electron diffraction from two standing waves with two different frequencies. The effects of increasing the frequency of the second laser beam and changing the laser amplitudes on the form and period of the Rabi oscillation are studied theoretically. The corresponding scattering probabilities for certain incident electron momenta are obtained by an analytical Rabi matrix and numerical solution of the Dirac equation. We show that at high intensities,≥ 10 20 W cm− 2, the process with an even number of photons involved in the Kapitza-Dirac effect can be used as a spin filter for free electrons. On the other hand, the process with an odd number photons and an electron with momentum along the laser polarization preserves the initia
In this report, we introduce the static coherent states (SCS) method for investigating quantum electron dynamics in a one-or two-electron laser-induced system. The SCS method solves the time-dependent Schr?dinger equation (TDSE) both in imaginary and real times on the basis of a static grid of coherent states (CSs). Moreover, we consider classical dynamics for the nuclei by solving their Newtonian equations of motion. By implementing classical nuclear dynamics, we compute the electronic-state potential energy curves of H 2+ in the absence and presence of an ultra-short intense laser field. We used this method to investigate charge migration in H 2+. In particular, we found that the charge migration time increased exponentially with inter-nu
We theoretically demonstrate the feasibility of producing electron beam splitter using Kapitza-Dirac diffraction on bichromatic standing waves which are created by the fundamental frequency and the third harmonic. The relativistic electron in Bragg regime absorbs three photons with frequency of w and emits a photon with frequency of 3w, four-photon Kapitza-Dirac effect. In this four-photon Kapitza-Dirac effect distinct spin effects arise in different polarizations of the third harmonic laser beam. It is shown that the shape of Rabi oscillation between initial and scattered states is changed and finds two unequal peaks. In circular polarization for fundamental and third harmonic, despite Rabi oscillation, the spin down electron in 0.56 fs in
We numerically solved the full-dimensional electronic time-dependent Schr\"{o} dinger equation for H with Born-Oppenheimer approximation under different sin -shaped and trapezoidal laser pulses at some different wavelengths, with 1 Wcm , 3 Wcm , and 6 Wcm intensity at 4.73 au and 7.0 au internuclear distances. Some structures such as complexity, minima, and oscillatory patterns appeared in the high-order harmonic generation (HHG) spectra are investigated in this work by considering the electron localization, electron nonadiabatic dynamics, spatially asymmetric of the HHG, and the Rabi frequency of the population of the ground and excited electronic states to better understand the origins of these structures in the HHG spectrum. We will c
The electronic properties, adsorption energies and energy barrier of sodium ion diffusion in B-doped graphyne (BGY) are studied by density functional theory (DFT) method. If some carbon atoms in pristine graphyne (GY) are substituted by boron atoms (one substitution per unit cell in this work), BGY is obtained which band structure and density of state (DOS) plots indicate a transition from a semiconductive state for GY to a metallic state for BGY. The calculated adsorption energy shows an improvement in the trigonal-like pore (T site) and hexagonal ring (H site) adsorption of BGY in compare to corresponding analog sites in GY. Comparing projected density of state (PDOS) plots before and after adsorption reveals charge transfer from sodium t
Contributions of the pre-ionized H 2 (PI-H 2) and ionized subsystems of the two-electron H 2 system to its high-order harmonic generation in eight-cycle sin 2-like ultrafast intense laser pulses are calculated and analyzed based on the solution of the time-dependent Schr?dinger equation for the one-dimensional two-electronic H 2 system with fixed nuclei. The laser pulses have λ= 390 and 532 nm wavelengths and I= 1? 10 14, 5? 10 14, 1? 10 15 and 5? 10 15 W cm− 2 intensities. It is found that at the two lower intensities, the PI-H 2 subsystem dominantly produces the HHG spectra. However, at the two higher intensities, both PI-H 2 and ionized subsystems contribute comparably to the HHG spectra. In the subsystem, the symmetry of the popul
In our previous report, we introduced a new version of Fermion coupled coherent states method (FCCS) which was especially suited for simulating the first symmetric spatial electronic state of two‐electron systems. In this manuscript, we report a complementary version for FCCS method to simulate both of the first symmetric and antisymmetric spatial electronic states of two‐electron systems. Moreover, the Gram–Schmidt orthogonalization process is employed to reach the excited states of the system. We apply this FCCS method and the original coupled coherent state method to simulate the energy of different electronic states of and , respectively. The results for the energy of computed electronic states of and show a pretty good con
The coupled coherent states method (CCS) has been optimized in order to remove the two complexities in the simulation of the ground state of electronic systems. These two complexities are the necessity of the energy restriction in the process of generating CS grid, and the essential refinement of the grid in each time-step. The optimized method which for the first time has been applied for simulation of the potential well of the ground state of one-electron systems such as 2 H+. The simulation results on the basis of a grid containing only 500 coherent states show a very good consistency with the exact curve. Implementing grids with more coherent states into the simulation would lead to a better consistency with the exact values.
We numerically solve the fully-dimensional electronic time-dependent Schr?dinger equation for an molecular ion. The occurrence of electron localization is investigated to better understand the complex patterns appearing in the high-order harmonic generation (HHG) spectrum. Our studies show that changing trends of electronic acceleration are affected by electron localization at large enough internuclear distances. This effect leads to the complex patterns in the HHG spectrum.
The underlying physics behind the molecular harmonic emission in relatively long sin 2-like laser pulses is investigated. We numerically solved the full-dimensional electronic time-dependent Schr?dinger equation beyond the Born-Oppenheimer approximation for simple molecular ion H 2+. The occurrence and the effect of electron localization, nonadiabatic redshift, and spatially asymmetric emission are evaluated to understand better complex patterns appearing in the high-order harmonic generation (HHG) spectrum. Results show that the complex patterns in the HHG spectrum originate mainly from a nonadiabatic response of the molecule to the rapidly changing laser field and also from a spatially asymmetric emission along the polarization direction.
A RELATIVISTIC DESCRIPTION OF THE KAPITZA-DIRAC EFFECT, WHICH REFERS TO ELECTRON SCATTERING AT STANDING LIGHT WAVES, IS STUDIED IN THE BRAGGREGIME WITH COUNTER PROPAGATING LINEARLY POLARIZED ELECTROMAGNETIC WAVES WITH THE SAME INTENSITY, WAVELENGTH. OUR RESULTS ARE BASED ON NUMERICAL SOLUTIONS OF THE TIME-DEPENDENT DIRAC EQUATIONIN MOMENTUMSPACE....
High-order harmonic generation (HHG) is investigated for and its isotopologues under seven and ten-cycle trapezoidal laser pulses at an 800 nm wavelength and I= 4? 10 14 W cm− 2 intensity. We numerically solved the full-dimensional electronic time-dependent Schr?dinger equation (TDSE) with and without the Born–Oppenheimer approximation (BO). We show that contribution to the HHG spectrum from the trailing edge of a trapezoidal laser pulse can result in a redshift and complexity in the total HHG spectrum. This effect can be removed by considering different laser pulse durations and nuclear motion that is not possible for sin 2 and Gaussian laser pulses. We have resolved the contributions to the redshift and other patterns in the HHG spec
Two different induced effects of a laser falling edge on high-order harmonic generation (HHG) are resolved by numerically solving the full-dimensional electronic time-dependent Schr?dinger equation beyond the Born–Oppenheimer approximation. The harmonic spectrum of and isotopes are compared to see the effects of a four-cycle falling edge of a 800 nm, 15-cycle trapezoidal laser pulse of I= 3 W cm− 2 intensity on harmonic emission spectrum. The harmonic emission at the laser falling part is negligible for due to ionization suppression, but considerable for . The falling edge of the laser pulse induces two effects on the HHG in . The first well-known effect is non-adiabatic frequency redshift of generated odd-order harmonics. The second
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