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Filatov, Michael,Min, Seung Kyu,Kim, Kwang S. American Chemical Society 2018 Journal of chemical theory and computation Vol.14 No.9
<P>In this work, a direct mixed quantum-classical dynamics approach is presented, which combines two new computational methodologies. The nuclear dynamics is solved by the decoherence-induced surface hopping based on the exact factorization (DISH-XF) method, which is derived from the exact factorization of the electronic-nuclear wave function and correctly describes quantum decoherence phenomena. The state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS, or SSR, for brevity) electronic structure method is based on ensemble density functional theory (eDFT) and provides correct description of real crossings between the ground and excited Born-Oppenheimer electronic states. The new combined approach has been applied to the excited-state nonadiabatic dynamics of the <I>trans</I>-penta-2,4-dieniminium cation (PSB3). The predicted S<SUB>1</SUB> lifetime of <I>trans</I>-PSB3, τ = 99 ± 51 fs, and the quantum yield of the cis conformation, ϕ = 0.63, agree with the results obtained previously in nonadiabatic molecular dynamics simulations performed with a variety of electronic structure methods and dynamics formalisms. Normal-mode analysis of the obtained classical nuclear trajectories suggests that only a few vibrational normal modes contribute to the nuclear wavepacket; where synchronization between several modes plays a dominant role for the outcome of photoisomerization.</P> [FIG OMISSION]</BR>
Filatov, Michael,Martí,nez, Todd J.,Kim, Kwang S. The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.31
<P>Ensemble density functional theory (DFT) furnishes a rigorous theoretical framework for describing the non-dynamic electron correlation arising from (near) degeneracy of several electronic configurations. Ensemble DFT naturally leads to fractional occupation numbers (FONs) for several Kohn-Sham (KS) orbitals, which thereby become variational parameters of the methodology. The currently available implementation of ensemble DFT in the form of the spin-restricted ensemble-referenced KS (REKS) method was originally designed for systems with only two fractionally occupied KS orbitals, which was sufficient to accurately describe dissociation of a single chemical bond or the singlet ground state of biradicaloid species. To extend applicability of the method to systems with several dissociating bonds or to polyradical species, more fractionally occupied orbitals must be included in the ensemble description. Here we investigate a possibility of developing the extended REKS methodology with the help of the generalized valence bond (GVB) wavefunction theory. The use of GVB enables one to derive a simple and physically transparent energy expression depending explicitly on the FONs of several KS orbitals. In this way, a version of the REKS method with four electrons in four fractionally occupied orbitals is derived and its accuracy in the calculation of various types of strongly correlated molecules is investigated. We propose a possible scheme to ameliorate the partial size-inconsistency that results from perfect spin-pairing. We conjecture that perfect pairing natural orbital (NO) functionals of reduced density matrix functional theory (RDMFT) should also display partial size-inconsistency.</P>
Theoretical modelling of the dynamics of primary photoprocess of cyclopropanone
Filatov, Michael,Min, Seung Kyu,Choi, Cheol Ho The Royal Society of Chemistry 2019 Physical chemistry chemical physics Vol.21 No.5
<P>Photodecomposition of cyclopropanone is investigated by static quantum chemical calculations and non-adiabatic molecular dynamics (NAMD) simulations. The quantum chemical calculations are carried out by an ensemble density functional theory (eDFT) method capable of delivering high quality results for the ground and excited electronic states of molecules with dissociating bonds. In the NAMD simulations, this method is combined with a novel trajectory surface hopping (TSH) methodology derived from the exact factorization of the electronic-nuclear wavefunction. An ultrafast biexponential decay of the S1 state of cyclopropanone is predicted, where the short (<I>ca.</I> 30 fs) decay time is due to the trajectories reaching the conical intersection (CI) seam on the first approach and the long (<I>ca.</I> 120 fs) decay time is due to recrossing of the CI seam. The experimentally observed dependence of the dissociation (C3H4O* → C2H4 + CO) quantum yield on the excitation wavelength is correctly reproduced by the NAMD simulations. The dependence is explained by the necessity to excite certain vibrational normal modes (<I>e.g.</I>, a ring stretching mode with the frequency of 769 cm<SUP>−1</SUP>) to break a lateral C-C bond remaining intact at the geometries of the CI seam.</P>
Filatov, Michael,Paolino, Marco,Min, Seung Kyu,Choi, Cheol Ho The Royal Society of Chemistry 2019 Chemical communications Vol.55 No.36
<P>A new family of light driven molecular rotary motors, which can be synthesized from easily available precursor compounds and which are capable of completing a full 360° revolution by two photoisomerization steps only, is proposed. The non-adiabatic molecular dynamic simulations show that the photoisomerization steps of the motor's working cycle occur on an ultrafast time scale (<I>ca.</I> 200-300 fs), have a very high quantum yield of isomerization (0.91-0.97), and display high selectivity of torsion in the same direction. It is expected that the new motor should remain operational at lower temperatures than the currently existing motors.</P>
Lee, In Seong,Filatov, Michael,Min, Seung Kyu American Chemical Society 2019 Journal of chemical theory and computation Vol.15 No.5
<P>The spin-restricted ensemble-referenced Kohn-Sham (REKS) method and its state-interaction state-averaged variant (SI-SA-REKS, or SSR) provide computational platform for seamless inclusion of multireference effects into the density functional calculations. The SSR method enables an accurate calculation of the vertical excitation energies for the molecules with multireference ground states and describes conical intersections between the ground and excited states with the accuracy matching the most sophisticated <I>ab initio</I> multireference wave function methods. In this work, the SSR method is formulated and implemented in the context of the long-range corrected density functional tight binding (LC-DFTB) approach. The new LC-DFTB/SSR method enables calculation of the excited electronic states and the S<SUB>1</SUB>/S<SUB>0</SUB> conical intersections of very large molecules. The LC-DFTB/SSR method is benchmarked against vertical excitation energies and conical intersection energies and geometries of several organic molecules with π/π* and <I>n</I>/π* transitions. It is demonstrated that the LC-DFTB/SSR method describes these molecules with reasonable accuracy, which can be considerably improved by a slight modification of the LC-DFTB spin polarization parameters.</P> [FIG OMISSION]</BR>
New Forms of CdSe: Molecular Wires, Gels, and Ordered Mesoporous Assemblies
Hudson, Margaret H.,Dolzhnikov, Dmitriy S.,Filatov, Alexander S.,Janke, Eric M.,Jang, Jaeyoung,Lee, Byeongdu,Sun, Chengjun,Talapin, Dmitri V. American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.9
<P>This work investigates the structure and properties of soluble chalcogenidocadmates, a molecular form of cadmium chalcogenides with unprecedented one-dimensional bonding motifs. The single crystal X-ray structure reveals that sodium selenocadmate consists of infinite one-dimensional wires of (Cd2Se3)(n)2(n-) charge balanced by Na+ and stabilized by coordinating solvent molecules. Exchanging the sodium cation with tetraethylammonium or didodecyldimethylammonium expands the versatility of selenocadmate by improving its solubility in a variety of polar and nonpolar solvents without changing the anion structure and properties. The introduction of a micelle-forming cationic surfactant allows for the templating of selenocadmate, or the analogous telluride species, to create ordered organic-inorganic hybrid CdSe or CdTe mesostructures. Finally, the interaction of selenocadmate 'wires' with Cd2+ ions creates an unprecedented gel-like form of stoichiometric CdSe. We also demonstrate that these low-dimensional CdSe species show characteristic semiconductor behavior, and can be used in photodetectors and field-effect transistors.</P>