Two-dimensional electronic-vibrational spectroscopic study of conical intersection dynamics: an experimental and electronic structure study.

The relaxation from the lowest singlet excited state of the triphenylmethane dyes, crystal violet and malachite green, is studied via two-dimensional electronic-vibrational (2DEV) spectroscopy. After excitation of the dyes at their respective absorption maxima, the ensuing excited state dynamics are tracked by monitoring the C[double bond, length as m-dash]C aromatic stretch. With the aid of electronic structure calculations, the observed transitions in the 2DEV spectra are assigned to specific geometries and a detailed story of the evolution of the nuclear wavepacket as it diffuses on the excited state potential energy surface (PES) and ultimately passes through the conical intersection is developed. Notably, it is revealed that the relaxation of the lowest singlet excited state involves intramolecular charge transfer while the nuclear wavepacket is on the excited state PES. Finally, through analyzing the center line slopes of the measured peaks, we show how both solvent motions and changes in the molecular dipole moment affect the correlation between electronic and vibrational degrees of freedom. This work clearly demonstrates the usefulness of 2DEV spectroscopy in following the motion of nuclear wavepackets after photoexcitation and in studying the interactions between the molecular dipole moment and surrounding solvent environment.

Energy Decomposition Analysis for Excimers Using Absolutely Localized Molecular Orbitals within Time-Dependent Density Functional Theory and Configuration Interaction with Single Excitations.

We present an improved energy decomposition analysis (EDA) scheme for understanding intermolecular interactions in delocalized excited states, especially in excimers. In the EDA procedure, excited states are treated with linear response theory such as configuration interaction singles (CIS) or time-dependent density functional theory (TDDFT), and absolutely localized molecular orbitals (ALMOs) are used to define the intermediate (frozen, excitonic coupling, and polarized) states. The intermolecular interaction energy is thereby separated into frozen, excitonic splitting, polarization, and charge transfer contributions. The excitonic splitting term describes the delocalization effect as two or more degenerate local excitations coupled with each other, which is often an important binding force in excimers. A maximum overlap state-tracking procedure is introduced to connect the initial fragment excitations to the constrained intermediate states and finally to the unconstrained delocalized states of the complex. The EDA scheme is applied to several excimer systems, including the He2* and Ne2* noble gas excimers, the doubly hydrogen-bonded 2-pyridone dimer, and the aromatic benzene and perylene excimers. We are able to gain some useful insights into the role each term is playing in the formation of these excimers, and the resulting method may also be useful for understanding a range of other complexes in excited states.

On the Computational Characterization of Charge-Transfer Effects in Noncovalently Bound Molecular Complexes.

Charge-transfer (CT) is an important binding force in the formation of intermolecular complexes, and there have been a variety of theoretical models proposed to quantify this effect. These approaches, which typically rely on a definition of a "CT-free" state based on a partition of the system, sometimes yield significantly different results for a given intermolecular complex. Two widely used definitions of the "CT-free" state, the absolutely localized molecular orbitals (ALMO) method (where only on-fragment orbital mixings are permitted) and the constrained density functional theory (CDFT) approach (where fragment electron populations are fixed), are carefully examined in this work. Natural bond orbital (NBO) and the regularized symmetry-adapted perturbation theory (SAPT) are also briefly considered. Results for the ALMO and CDFT definitions of CT are compared on a broad range of model systems, including hydrogen-bonding systems, borane complexes, metal-carbonyl complexes, and complexes formed by water and metal cations. For most of these systems, CDFT yields a much smaller equilibrium CT energy compared to that given by the ALMO-based definition. This is mainly because the CDFT population constraint does not fully inhibit CT, which means that the CDFT "CT-free" state is in fact CT-contaminated. Examples of this contamination include (i) matching forward and backward donation (e.g., formic acid dimer) and (ii) unidirectional CT without changing fragment populations. The magnitude of the latter effect is quantified in systems such as the water dimer by employing a 3-space density constraint in addition to the orbital constraint. Furthermore, by means of the adiabatic EDA, it is shown that several observable effects of CT, such as the "pyramidalization" of the planar BH3 molecule upon the complexation with Lewis bases, already appear on the "CT-free" CDFT surface. These results reveal the essential distinctions between the ALMO and CDFT definitions of CT and suggest that the former is more consistent with accepted understanding of the role of CT in intermolecular binding.

Energy decomposition analysis for exciplexes using absolutely localized molecular orbitals.

An energy decomposition analysis (EDA) scheme is developed for understanding the intermolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized molecular orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexes (e.g., formamide-water, pyridine/pyrimidine-water) and halide (F-, Cl-)-water clusters that involve charge-transfer-to-solvent excitations.

Simulating the absorption spectra of helium clusters (N = 70, 150, 231, 300) using a charge transfer correction to superposition of fragment single excitations.

Simulations of the n = 2 absorption spectra of HeN (N = 70, 150, 231, 300) clusters are reported, with nuclear configurations sampled by path integral molecular dynamics. The electronic structure is treated by a new approach, ALMO-CIS+CT, which is a formulation of configuration interaction singles (CIS) based on absolutely localized molecular orbitals (ALMOs). The method generalizes the previously reported ALMO-CIS model [K. D. Closser et al. J. Chem. Theory Comput. 11, 5791 (2015)] to include spatially localized charge transfer (CT) effects. It is designed to recover large numbers of excited states in atomic and molecular clusters, such as the entire n = 2 Rydberg band in helium clusters. ALMO-CIS+CT is shown to recover most of the error caused by neglecting charge transfer in ALMO-CIS and has comparable accuracy to standard CIS for helium clusters. For the n = 2 band, CT stabilizes states towards the blue edge by up to 0.5 eV. ALMO-CIS+CT retains the formal cubic scaling of ALMO-CIS with respect to system size. With improvements to the implementation over that originally reported for ALMO-CIS, ALMO-CIS+CT is able to treat helium clusters with hundreds of atoms using modest computing resources. A detailed simulation of the absorption spectra associated with the 2s and 2p bands of helium clusters up to 300 atoms is reported, using path integral molecular dynamics with a spherical boundary condition to generate atomic configurations at 3 K. The main features of experimentally reported fluorescence excitation spectra for helium clusters are reproduced.

Association of human leukocyte antigen DP/DQ gene polymorphisms with chronic hepatitis B in Chinese Han and Uygur populations.

Several genome-wide association studies (GWAS) have shown that human leukocyte antigen (HLA) DP/DQ gene polymorphisms are associated with susceptibility to chronic hepatitis B virus (HBV) infection. We clarified the roles of the HLA-DP/DQ gene in HBV infection in different nationalities. Three single nucleotide polymorphisms (SNPs) in HLA-DP (rs9277471, rs9277535 and rs9277542) and the SNP rs9272346 in HLA-DQ were studied. In total, 779 patients were recruited to this study, including 400 Chinese Han and 399 Uygurs. The rs9277535 variant genotypes were directly associated with HBV persistence compared to healthy controls in an additive model of the Chinese Han population (odds ratio [OR]=1.88, 95% confidence interval [CI]=1.03-3.41, P=0.040), and in a recessive model of the Chinese female population (OR=2.02, 95% CI=1.26-3.24, P=0.003). In addition, rs9277471 and rs9277542 variant genotypes significantly decreased the risk of HBV infection compared to healthy controls in an additive model of the Chinese Han population (OR=0.53, 95% CI=0.29-0.98, P=0.042; OR=0.53, 95% CI=0.29-0.97, P=0.039) and in a dominant model of the Chinese female population (OR=0.50, 95% CI=0.31-0.80, P=0.004; OR=0.49, 95% CI=0.31-0.79, P=0.003). The GG genotype of rs9277346 was associated with HBV infection in the Chinese Han population (additive model: OR=0.38, 95%CI=017-0.82, P=0.014; recessive model: OR=0.41, 95% CI=0.19-0.86, P=0.019) and in males (additive model: OR=0.31, 95% CI=0.14-0.65, P=0.002; dominant model: OR=0.65, 95% CI=0.43-0.97, P=0.034; recessive model: OR=0.36, 95% CI=0.18-0.73, P=0.005). In addition, allele G of rs9277346 was marginally related to a reduction in risk for HBV infection in the Uygur population. Our study suggests that HLA-DP/DQ polymorphisms can affect susceptibility and resistance to HBV infection in Chinese populations, and are possibly linked to race and sex.

Superposition of Fragment Excitations for Excited States of Large Clusters with Application to Helium Clusters.

We develop a local excited-state method, based on the configuration interaction singles (CIS) wave function, for large atomic and molecular clusters. This method exploits the properties of absolutely localized molecular orbitals (ALMOs), which strictly limits the total number of excitations, and results in formal scaling with the third power of the system size for computing the full spectrum of ALMO-CIS excited states. The derivation of the equations and design of the algorithm are discussed in detail, with particular emphasis on the computational scaling. Clusters containing ∼500 atoms were used in evaluating the scaling, which agrees with the theoretical predictions, and the accuracy of the method is evaluated with respect to standard CIS. A pioneering application to the size dependence of the helium cluster spectrum is also presented for clusters of 25-231 atoms, the largest of which results in the computation of 2310 excited states per sampled cluster geometry.

A Guided Stochastic Energy-Domain Formulation of the Second Order Møller-Plesset Perturbation Theory.

We develop an alternative formulation in the energy-domain to calculate the second order Møller-Plesset (MP2) perturbation energies. The approach is based on repeatedly choosing four random energies using a nonseparable guiding function, filtering four random orbitals at these energies, and averaging the resulting Coulomb matrix elements to obtain a statistical estimate of the MP2 correlation energy. In contrast to our time-domain formulation, the present approach is useful for both quantum chemistry and real-space/plane wave basis sets. The scaling of the MP2 calculation is roughly linear with system size, providing a useful tool to study dispersion energies in large systems. This is demonstrated on a structure of 64 fullerenes within the SZ basis as well as on silicon nanocrystals using real-space grids.