Christel M. Marian

Bio: Christel M. Marian is an academic researcher from University of Düsseldorf. The author has contributed to research in topics: Excited state & Intersystem crossing. The author has an hindex of 47, co-authored 225 publications receiving 8434 citations. Previous affiliations of Christel M. Marian include Autonomous University of Madrid & Ludwig Maximilian University of Munich.

Spin–orbit coupling and intersystem crossing in molecules

Abstract: Many light-induced molecular processes involve a change in spin state and are formally forbidden in non-relativistic quantum theory. To make them happen, spin–orbit coupling (SOC) has to be invoked. Intersystem crossing (ISC), the nonradiative transition between two electronic states of different multiplicity, plays a key role in photochemistry and photophysics with a broad range of applications including molecular photonics, biological photosensors, photodynamic therapy, and materials science. Quantum chemistry has become a valuable tool for gaining detailed insight into the mechanisms of ISC. After a short introduction highlighting the importance of ISC and a brief description of the relativistic origins of SOC, this article focusses on approximate SOC operators for practical use in molecular applications and reviews state-of-the-art theoretical methods for evaluating ISC rates. Finally, a few sample applications are discussed that underline the necessity of studying the mechanisms of ISC processes beyond qualitative rules such as the El-Sayed rules and the energy gap law. © 2011 John Wiley & Sons, Ltd.

Spin-Vibronic Mechanism for Intersystem Crossing

Abstract: Intersystem crossing (ISC), formally forbidden within nonrelativistic quantum theory, is the mechanism by which a molecule changes its spin state. It plays an important role in the excited state decay dynamics of many molecular systems and not just those containing heavy elements. In the simplest case, ISC is driven by direct spin–orbit coupling between two states of different multiplicities. This coupling is usually assumed to remain unchanged by vibrational motion. It is also often presumed that spin-allowed radiationless transitions, i.e. internal conversion, and the nonadiabatic coupling that drives them, can be considered separately from ISC and spin–orbit coupling owing to the vastly different time scales upon which these processes are assumed to occur. However, these assumptions are too restrictive. Indeed, the strong mixing brought about by the simultaneous presence of nonadiabatic and spin–orbit coupling means that often the spin, electronic, and vibrational dynamics cannot be described independe...

A new pathway for the rapid decay of electronically excited adenine.

Abstract: Combined density functional and multireference configuration interaction methods have been used to calculate the electronic spectrum of 9H-adenine, the most stable tautomer of 6-aminopurine. In addition, constrained minimum energy paths on excited potential energy hypersurfaces have been determined along several relaxation coordinates. The minimum of the first [n→π*]1 state has been located at an energy of 4.54eV for a nuclear arrangement in which the amino group is pyramidal whereas the ring system remains planar. Close by, another minimum on the S1 potential energy hypersurface has been detected in which the C2 center is deflected out of the molecular plane and the electronic character of S1 corresponds to a nearly equal mixture of [π→π*]1 and [n→π*]1 configurations. The adiabatic excitation energy of this minimum amounts to 4.47eV. Vertical and adiabatic excitation energies of the lowest n→π* and π→π* transitions as well as transition moments and their directions are in very good agreement with experim...

Performance of the Density Functional Theory/Multireference Configuration Interaction Method on Electronic Excitation of Extended π-Systems.

Abstract: The combined density functional theory/multireference configuration interaction (DFT/MRCI) method [Grimme and Waletzke. J. Chem. Phys. 1999, 111, 5645] has been employed to study the 1La and 1Lb states of linear polyacenes and the low-lying triplet and singlet states of linear polyenes and diphenyl-polyenes. We have systematically investigated the dependence of the electronic state properties on technical parameters of the calculations such as the atomic orbital basis set or the geometry optimization approach. The choice of basis set appears to be of minor importance whereas the excitation energies of the polyenes are quite sensitive to the ground-state geometry parameters. The DFT/MRCI energies at the B3-LYP optimized geometries systematically underestimate the experimental values, but we do not observe a bias toward one or the other type of state. The energy gaps between the electronically excited states are reproduced very well. In particular, this applies also to the first excited singlet 2 1Ag− and t...

The general utility lattice program (GULP)

Abstract: The General Utility Lattice Program (GULP) has been extended to include the ability to simulate polymers and surfaces, as well as adding many other new features, and the current status of the program is fully documented. Both the background theory is described, as well as providing a concise review of some of the previous applications in order to demonstrate the range of its use. Examples are presented of work performed using the new compatibilities of the software, including the calculation of Born effective charges, mechanical properties as a function of applied pressure, calculation of frequency-dependent dielectric data, surface reconstructions of calcite and the performance of a linear-scaling algorithm for bond-order potentials.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg