Time‐dependent density functional theory study of electronic spectrum property for carbazolyl–pyridinyl alternating copolymers

Three A‐B‐type fluorescent copolymers comprised of alternating carbazolyl and pyridinyl units, poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(3,5‐pyridinyl))](PEHCP‐35), poly[(2,7‐(N‐(2‐ethylhexyl)carbazolyl)‐alt‐(2,6‐pyridinyl))] (PEHCP‐26) and poly[(2,7‐(N‐(2‐ethyl‐hexyl)carbazolyl)‐alt‐(2,5‐pyridinyl))] (PEHCP‐25), are studied by means of the density functional theory (DFT/B3LYP/6‐31G). Based on the optimized geometries, the optical properties are calculated by employing time‐dependent density functional theory (TD‐DFT). The bandgaps and optical properties are saturated quickly in PEHCP‐35 and PEHCP‐26. It is known from experiment that PEHCP‐25 is actually an oligomer with a polymerization degree of 4. So the tetramers of PEHCP‐35, PEHCP‐26, and PEHCP‐25 are adopted to study the electronic and optical properties, and the calculated results are in close agreement with experiment. The calculated bandgaps of copolymers obtained from two ways, i.e., HOMO–LUMO gaps and the lowest excitation energies, decrease in the following order PEHCP‐35 > PEHCP‐26 > PEHCP‐25, the same trend as the data obtained from the edge of the electric band but different from the electrochemically obtained data from experiment (PEHCP‐25 > PEHCP‐26 > PEHCP‐35). The outcomes showed that, when excited, a charge transfer from carbazolyl unit to pyridinyl unit occurs, and the lumophor is mainly carbazolyl units. The UV absorption and emission wavelengths both exhibit bathochromic shifts: PEHCP‐35 < PEHCP‐26 < PEHCP‐25. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Time‐dependent wave packet approach to Rabi oscillation in strong laser field

The phenomenon of Rabi oscillation is obtained in the investigation of the NO multiphoton ionization (MPI) in femtosecond laser fields. The “split operator‐Fourier transform” method of wave packet propagation is used in the representation of Rabi oscillation of population in each electronic state of NO molecule. The origin of Rabi oscillation and the effect on multiphoton ionization is analyzed. The high‐frequency oscillation riding on the top of Rabi oscillation is attributed to the nonrotating wave component in strong laser fields. Also illustrated is that through adjusting the pump‐probe delay time and the laser intensity appropriately the control of the ionization yield can be realized. This idea may be important for the laser control of chemical reaction. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 30–36, 2003     

Time‐dependent density functional theory study on direction‐dependent electron and hole transfer processes in molecular systems

We report on real‐time time‐dependent density functional theory calculations on direction‐dependent electron and hole transfer processes in molecular systems. As a model system, we focus on α‐sulfur. It is shown that time scale of the electron transfer process from a negatively charged S₈ molecule to a neighboring neutral monomer is comparable to that of a strong infrared‐active molecular vibrations of the dimer with one negatively charged monomer. This results in a strong coupling between the electrons and the nuclei motion which eventually leads to S₈ ring opening before the electron transfer process is completed. The open‐ring structure is found to be stable. The similar infrared‐active peak in the case of hole transfer, however, is shown to be very weak and hence no significant scattering by the nuclei is possible. The presented approach to study the charge transfer processes in sulfur has direct applications in the increasingly growing research field of charge transport in molecular systems. © 2017 Wiley Periodicals, Inc.     

Time‐dependent molecular fields created by the interaction of an external electromagnetic field with a molecular system

When an external, time‐dependent field interacts with a molecular system various phenomena may take place. However, concentrating on a region close enough to a point of conical intersection, we find that this external field builds up a field similar to an electromagnetic field formed on the one hand by Field‐Dressed nonadiabatic coupling terms which are reminiscent of the Maxwell–Lorentz Vector potentials, and on the other hand via a scalar potential formed by the dipole‐interaction with an external field. In this article, we show that this new field, to be termed Molecular Field, is characterized by several spatial and space‐time Field‐Dressed Curl equations and one, single, space‐time Field‐Dressed Divergence equation. These equations are then shown to yield, just as in the general theory of electromagnetism, the corresponding Field‐Dressed Wave Equations. This achievement could be materialized employing the (1,2) antisymmetric matrix elements of any of the 2×2 dimensional Field‐Dressed nonadiabatic coupling matrices. © 2014 Wiley Periodicals, Inc.     

Theoretical study of electronic states of N22+in an intense radiation field

The Floquet states of N(2) (2+) created by the interactions of the six lowest singlet (1 (1)Sigma(g) (+), 1 (1)Delta(g), 2 (1)Sigma(g) (+), 1 (1)Pi(u), 1 (1)Pi(g), and 1 (1)Sigma(u) (-)) states of the dication with intense (0.4 x 10(13) Wcm(2)) radiation have been studied using the recently developed multireference configuration interaction method with single and double excitations (MRCISD)-based approach. The adiabatic Floquet state coinciding near its minimum with the initial X (1)Sigma(g) (+) ground state and asymptotically correlating with A (1)Pi(u) (m = -1), i.e., with one less photon in the dressed state, is expected to be metastable, as is the ground state in the absence of a field, but to support up to the v(max) = 12 quasibound vibrational level in comparison with v(max) = 11 in the parent field-free X (1)Sigma(g) (+) ground state. The tunneling lifetimes of the highest vibrational levels in this adiabatic Floquet state are predicted to be several orders longer than those in the parent field-free state. Analysis of the complete basis set limit extrapolated MRCISD potential energy curve of the field-free X (1)Sigma(g) (+) state of N(2) (2+) calculated in the present work (R(e) = 1.130 A, omega(e) = 2011 cm(-1), omega(e)x(e) = 26.1 cm(-1)) is in good agreement with spectroscopic experimental data. Calculations on the field-free A (1)Pi(u) state (T(e) = 12 106 cm(-1), R(e) = 1.252 A, omega(e) = 1438 cm(-1), omega(e)x(e) = 23.5 cm(-1)) generally support earlier theoretical work and do not support reported experimental values.     

A simple model of atomic collision in the presence of an intense radiation field: A comparison test for gauge invariant vs. conventional quantum transition probabilities

A simple model mimicking the collision between two atomic partners in the presence of an intense radiation field is investigated according to a two-state, non perturbative approach, to put in quantitative evidence inadequacies in both transition probability and cross section arising from the use of transition amplitudes which are not gauge-invariant.     

Spin-Free quantum chemistry. XXII. Multiconfiguration self-consistent field theory

Second order MCSCF theory is presented in a unitary group formulation for any multiplicity without spin projection. Its reduction to lower order theory is discussed, as well as its extension through the use of effective Hamiltonians.     

Time-dependent variational principle in quantum field theory

This paper proposes a direct, quantum-mechanical definition for Γ (effective action) using a two-step procedure for applying the variational principle to time-dependent quantum problems.     

Time‐dependent density functional theory studies of the electronic absorption spectra of metallophthalocyanines of group IVA

Time‐dependent density functional theory (TD‐DFT) calculations were carried out in a comparative study of the electronic absorption spectra of lead(II) phthalocyaninate (PbPc), tin(II) phthalocyaninate (SnPc), tin(IV) dichlorophalocyaninate (PcSnCl₂), germanium(II) phthalocyaninate (GePc), and germanium (IV) dichlorophalocyaninate (PcGeCl₂) with the B3LYP method and LANL2DZ basis set. Our calculated bands correspond well with the experimental results. The electronic natures of all the bands in the absorption spectra are assigned and analyzed comparatively according to the calculated electronic transition contributions. With the increase of the dielectric constant from CHCl₃ to DMSO, all the electronic absorption bands are somewhat red shift, consistent with the shift rules measured experimentally. The radius of the central metals has great influence to the absorption spectra, especially for the B bands. The influence of the radius of the central metals to the absorption spectra of PcSnCl₂ and PcGeCl₂ is smaller than to the spectra of the nonplanar MPcs (M = Pb, Sn, and Ge). Axial ligands also greatly changed the electronic absorption spectra due to the change of the orbital energy level and the molecular symmetry. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Ionization and dissociation of CH3I in intense laser field

The ionization-dissociation of methyl iodide in intense laser field has been studied using a reflection time-of-flight mass spectrometry (RTOF-MS), at a laser intensity of < or =6.6x10(14) W/cm(2), lambda=798 nm, and a pulse width of 180 fs. With the high resolution of RTOF-MS, the fragment ions with the same M/z but from different dissociation channels are resolved in the mass spectra, and the kinetic energy releases (KERs) of the fragment ions such as I(q+) (q=1-6), CH(m) (+) (m=0-3), C(2+), and C(3+) are measured. It is found that the KERs of the fragment ions are independent of the laser intensity. The fragments CH(3) (+) and I(+) with very low KERs (<1 eV for CH(3) (+) and <0.07 eV for I(+)) are assigned to be produced by the multiphoton dissociation of CH(3)I(+). For the fragments CH(3) (+) and I(+) from CH(3)I(2+), they are produced by the Coulomb explosion of CH(3)I(2+) with the interaction from the covalent force of the remaining valence electrons. The split of the KER of the fragments produced from CH(3)I(2+) dissociation is observed experimentally and explained with the energy split of I(+)((3)P(2)) and I(+)((3)P(0,1)). The dissociation CH(3)I(3+)-->CH(3) (+)+I(2+) is caused by Coulomb explosion. The valid charge distance R(c) between I(2+) and CH(3) (+), at which enhanced ionization of methyl iodide occurs, is obtained to be 3.7 A by the measurements of the KERs of the fragments CH(3) (+) and I(2+). For the CH(3)I(n+) (n> or =3), the KERs of the fragment ions CH(3) (p+) and I(q+) are attributed to the Coulomb repulsion between CH(3) (p+) and I(q+) from R(c) approximately 3.7 A. The dissociation of the fragment CH(3) (+) is also discussed. By the enhanced ionization mechanism and using the measured KER of I(q+), all the possible Coulomb explosion channels are identified. By comparing the abundance of fragment ions in mass spectrum, it is found that the asymmetric dissociation channels with more charges on iodine, q>p, are the dominant channels.     

Time‐dependent schrödinger equation with Markovian outgoing wave boundary conditions: Applications to quantum tunneling dynamics and photoionization

Markovian outgoing wave boundary conditions are introduced as an approximate method to reduce the size of the computational grid for time integration of the time‐dependent Schrödinger equation. The ratio and polynomial methods developed as open boundary conditions are applied to the wave function at the boundaries of the computational grid. This computational method is used to study the wave packet dynamics for a metastable well, a double well, and strong‐field ionization of a model atom. Accurate results demonstrate that this method can significantly reduce the number of grid points required in a dynamical calculation for quantum dynamical problems. © 2012 Wiley Periodicals, Inc.