Simulating the HeI photoelectron spectrum of Cl2O with new full-dimensional adiabatic potential energy surfaces of Cl2O(X̃1A1), Cl2O+(X̃2B1), and Cl2O+(C̃2A2) and a three-state diabatic potential energy matrix of Cl2O+(Ã2B2, B̃2A1, and 22A1): a quantum mechanical study.

To interpret the HeI photoelectron spectrum of Cl2O (involving four lowest electronic states of Cl2O+), in this work we first constructed the associated adiabatic full-dimensional potential energy surfaces (PESs) of Cl2O(X̃1A1), Cl2O+(X̃2B1), and Cl2O+(C̃2A2) and a diabatic potential energy matrix (PEM) of Cl2O+(Ã2B2, B̃2A1, and 22A1) using the explicitly correlated internally contracted multi-reference configurational interaction with Davidson correction (MRCI-F12+Q) and neural network methods. Particularly for the Ã2B2, B̃2A1, and 22A1 states of Cl2O+ coupled in terms of conical intersection, their diabatization is achieved by the neural network approach based merely on the associated adiabatic energies. With the help of newly constructed adiabatic PESs and the diabatic PEM, the HeI photoelectron spectrum of Cl2O is further computed quantum mechanically. The calculated photoelectron spectrum is found to be in good accord with experiment. The mode specificity in the HeI photoelectron bands of Cl2O is analyzed in detail.

Association Between Hepatocellular Carcinoma and Type 2 Diabetes Mellitus in Chinese Hepatitis B Virus Cirrhosis Patients: A Case-Control Study.

BACKGROUND Whether the presence of type 2 diabetes mellitus (T2DM) increases the risk of hepatocellular carcinoma (HCC) in hepatitis B virus (HBV) cirrhosis patients is controversial. We conducted a retrospective case-control study to evaluate this issue. MATERIAL AND METHODS We considered all patients diagnosed with HBV-related liver cirrhosis at our hospital from July 2011 to June 2014. The case (n=91) and control (n=91) groups were HBV cirrhosis patients with and without T2DM, respectively. They were matched at a ratio of 1: 1 according to the individual age (±2 years) and same sex and Child-Pugh score. RESULTS None of the baseline data were significantly different between the 2 groups. The percentage of HCC was similar between the 2 groups (case versus control group: 34.1% versus 46.2%, P=0.13). In the case group, sex (P=0.002), alkaline phosphatase (P<0.001), g-glutamine transferase (P=0.001), and sodium (P=0.003) were associated with the risk of HCC. In the control group, platelet (P=0.041), alanine aminotransferase (P=0.034), aspartate aminotransferase (P=0.026), alkaline phosphatase (P<0.001), and γ-glutamine transferase (P<0.001) were associated with the risk of HCC. CONCLUSIONS T2DM may not be a risk factor for the presence of HCC in HBV cirrhosis.

Calculations of the active mode and energetic barrier to electron attachment to CF3 and comparison with kinetic modeling of experimental results.

To provide a deeper understanding of the kinetics of electron attachment to CF3, the six-dimensional potential energy surfaces of both CF3 and CF3- were developed by fitting ∼3000 ab initio points per surface at the AE-CCSD(T)-F12a/AVTZ level using the permutation invariant polynomial-neural network (PIP-NN) approach. The fitted potential energy surfaces for CF3 and CF3- had root mean square fitting errors relative to the ab initio calculations of 1.2 and 1.8 cm-1, respectively. The main active mode for the crossing between the two potential energy surfaces was identified as the umbrella bending mode of CF3 in C3v symmetry. The lowest energy crossing point is located at RCF = 1.306 Å and θFCF = 113.6° with the energy of 0.051 eV above the minimum of the CF3 electronic surface. This value is only slightly larger than the experimental data 0.026 ± 0.01 eV determined by kinetic modeling of electron attachment to CF3. The small discrepancy between the theoretical and experimentally measured values is analyzed.

Full-Dimensional Quantum Calculations of Vibrational Levels of NH4(+) and Isotopomers on An Accurate Ab Initio Potential Energy Surface.

Vibrational energy levels of the ammonium cation (NH4(+)) and its deuterated isotopomers are calculated using a numerically exact kinetic energy operator on a recently developed nine-dimensional permutation invariant semiglobal potential energy surface fitted to a large number of high-level ab initio points. Like CH4, the vibrational levels of NH4(+) and ND4(+) exhibit a polyad structure, characterized by a collective quantum number P = 2(v1 + v3) + v2 + v4. The low-lying vibrational levels of all isotopomers are assigned and the agreement with available experimental data is better than 1 cm(-1).

Quantum Dynamics of Vinylidene Photodetachment on an Accurate Global Acetylene-Vinylidene Potential Energy Surface.

Vinylidene is a high-energy isomer of acetylene, and the rearrangement of bonds in the two species serves as a prototype for isomerization reactions. Here, a full-dimensional quantum mechanical study of the vinylidene vibration is carried out on a recently developed global acetylene-vinylidene potential energy surface by simulating the photodetachment dynamics of the vinylidene anion. Several low-lying vibrational levels of the anion were first determined on a new ab initio based potential energy surface, and their photoelectron spectra were obtained within the Condon approximation. The vibrational features of the vinylidene isomer are found to agree well with the experiment in both positions and intensities, validating the global acetylene-vinylidene potential energy surface.

Relativistic configuration interaction calculation on the ground and excited states of iridium monoxide.

We present the fully relativistic multi-reference configuration interaction calculations of the ground and low-lying excited electronic states of IrO for individual spin-orbit component. The lowest-lying state is calculated for Ω = 1/2, 3/2, 5/2, and 7/2 in order to clarify the ground state of IrO. Our calculation suggests that the ground state is of Ω = 1/2, which is highly mixed with (4)Σ(-) and (2)Π states in Λ - S notation. The two low-lying states 5/2 and 7/2 are nearly degenerate with the ground state and locate only 234 and 260 cm(-1) above, respectively. The equilibrium bond length 1.712 Å and the harmonic vibrational frequency 903 cm(-1) of the 5/2 state are close to the experimental measurement of 1.724 Å and 909 cm(-1), which suggests that the 5/2 state should be the low-lying state that contributes to the experimental spectra. Moreover, the electronic states that give rise to the observed transition bands are assigned for Ω = 5/2 and 7/2 in terms of the obtained excited energies and oscillator strengths.

Near spectroscopically accurate ab initio potential energy surface for NH4(+) and variational calculations of low-lying vibrational levels.

A nine-dimensional potential energy surface (PES) for the ammonium cation has been constructed by fitting ∼30 000 AE-CCSD(T)-F12a/cc-pCVTZ-F12 points up to 32 262 cm(-1) (4.0 eV) from the minimum. The fitting using the permutation invariant polynomial-neural network method has high fidelity, with a root-mean-square error of merely 2.34 cm(-1). The low-lying vibrational energy levels of NH4(+) have been determined quantum mechanically using both Jacobi and normal coordinates, and the fundamental frequencies are in excellent agreement with available experimental data.

New schemes for internally contracted multi-reference configuration interaction.

In this work we present a new internally contracted multi-reference configuration interaction (MRCI) scheme by applying the graphical unitary group approach and the hole-particle symmetry. The latter allows a Distinct Row Table (DRT) to split into a number of sub-DRTs in the active space. In the new scheme a contraction is defined as a linear combination of arcs within a sub-DRT, and connected to the head and tail of the DRT through up-steps and down-steps to generate internally contracted configuration functions. The new scheme deals with the closed-shell (hole) orbitals and external orbitals in the same manner and thus greatly simplifies calculations of coupling coefficients and CI matrix elements. As a result, the number of internal orbitals is no longer a bottleneck of MRCI calculations. The validity and efficiency of the new ic-MRCI code are tested by comparing with the corresponding WK code of the MOLPRO package. The energies obtained from the two codes are essentially identical, and the computational efficiencies of the two codes have their own advantages.

Toward spectroscopically accurate global ab initio potential energy surface for the acetylene-vinylidene isomerization.

A new full-dimensional global potential energy surface (PES) for the acetylene-vinylidene isomerization on the ground (S0) electronic state has been constructed by fitting ∼37,000 high-level ab initio points using the permutation invariant polynomial-neural network method with a root mean square error of 9.54 cm(-1). The geometries and harmonic vibrational frequencies of acetylene, vinylidene, and all other stationary points (two distinct transition states and one secondary minimum in between) have been determined on this PES. Furthermore, acetylene vibrational energy levels have been calculated using the Lanczos algorithm with an exact (J = 0) Hamiltonian. The vibrational energies up to 12,700 cm(-1) above the zero-point energy are in excellent agreement with the experimentally derived effective Hamiltonians, suggesting that the PES is approaching spectroscopic accuracy. In addition, analyses of the wavefunctions confirm the experimentally observed emergence of the local bending and counter-rotational modes in the highly excited bending vibrational states. The reproduction of the experimentally derived effective Hamiltonians for highly excited bending states signals the coming of age for the ab initio based PES, which can now be trusted for studying the isomerization reaction.

New implementation of the configuration-based multi-reference second order perturbation theory.

We present an improved version of the configuration-based multi-reference second-order perturbation approach (CB-MRPT2) according to the formulation of Lindgren on perturbation theory of a degenerate model space. This version involves a reclassification of the perturbation functions and new algorithms to calculate matrix elements in the perturber energy expressions utilizing the graphical unitary group approach and the hole-particle symmetry. The diagonalize-then-perturb (DP), including Rayleigh-Schrödinger and Brillouin-Wigner, and diagonalize-then-perturb-then-diagonalize (DPD) modes have been implemented. The new CB-MRPT2 method is applied to several typical and interesting systems: (1) the vertical excitation energies for several states of CO and N(2), (2) energy comparison and timing of the ground state of C(4)H(6), (3) the quasi-degeneracy of states in LiF, (4) the intruder state problems of AgH, and (5) the relative energies of di-copper-oxygen-ammonia complex isomers. The results indicate that the computational accuracy and efficiency of the presented methods are competitive and intruder-free. It should be emphasized that the DPD method rectifies naturally the shortcomings of LiF potential energy curves constructed by the original second order complete active space perturbation theory (CASPT2), without having to recourse to the so-called state mixture. Unlike CASPT2, the new methods give the same energy ordering for the two di-copper-oxygen-ammonia isomers as the previous multi-reference configuration interaction with single and double excitations methods. The new CB-MRPT2 method is shown to be a useful tool to study small to medium-sized systems.

Global ab initio potential energy surfaces for both the ground (X̃1A') and excited (Ã1A'') electronic states of HNO and vibrational states of the Renner-Teller Ã1A''-X̃1A' system.

The global potential energy surfaces for both the ground (X̃(1)A(')) and excited (Ã(1)A('')) electronic states of the HNO molecule have been constructed by three-dimensional cubic spline interpolation of more than 17,000 ab initio points, which have been calculated at the internal contracted multi-reference configuration interaction level with the Davidson correction using an augmented correlation-consistent polarized valence quadruple zeta basis set. The low-lying vibrational energy levels for the two electronic states of HNO have also been calculated on our potential energy surfaces including the diagonal Renner-Teller terms. The calculated results have shown a good agreement with the experimental vibrational frequencies of HNO and its isotopomers.

Electronic structure calculations of low-lying electronic states of O3.

Configuration-based multi-reference second order perturbation theory (CB-MRPT2) and multi-reference configuration interaction with single and double excitations (MRCISD) have been used to calculate the bending and dissociation potential energy curves (PECs) of ozone. Based on these PECs, equilibrium structures, vertical and adiabatic transition energies of the ground state and several low-lying excited states, as well as intersections and avoided crossings among the states displayed on the PECs are investigated. The energy separation of the open and ring structures and the dissociation energy of the ground state X(1)A(1) are determined by reference-selected MRCISD. Furthermore, one-dimensional cuts along the dissociation reaction coordinate for the lowest four electronic states of O(3) with (1)A' symmetry and possible pre-dissociations are studied. The Hartley band may be pre-dissociable, and the pre-dissociation limit is found to be 3871 cm(-1), which corresponds to symmetric stretching quanta n(ss) ≈ 6.

Potential energy curves and interpretation of electronic spectrum of the rhodium monoxide.

Potential energy curves of 17 electronic states of rhodium monoxide (RhO) are calculated by multireference configuration interaction with single and double excitations (MRCISD). The ground state of RhO is determined to be a (4)Sigma(-) state with equilibrium bond length of 1.710 A and harmonic vibrational frequency of 825 cm(-1) at the MRCISD level of theory. It dissociates into Rh((4)F)+O((3)P) with a dissociation energy of 3.77/4.26 eV (MRCISD/MRCISD+Q), which is in agreement with the experimental value of 4.19+/-0.43 eV. Two low-lying excited states a (2)Sigma(-) and b(2)Pi are located at 4152 and 7154 cm(-1) above the ground state. The b(2)Pi with the adjacent (2)Delta, (4)Delta, and (2)Pi(II) states can be strongly coupled via spin-orbit interaction leading to a large splitting between b (2)Pi(3/2)-b (2)Pi(1/2) states with the value of 2422 cm(-1), which is comparable with the experimental value of 2400 cm(-1). Two higher doublets, c(2)Pi and d(2)Pi, have the same dominant configuration, 10sigma(2)11sigma(2)12sigma(1)5pi(4)6pi(3)2delta(3), and their transitions to the ground state, i.e., c(2)Pi-->(4)Sigma(-) and d(2)Pi-->(4)Sigma(-), correspond to the two visible bands of RhO.

The potential energy curves of low-lying electronic states of S2O.

Potential energy curves (PECs) of the symmetric and asymmetric bent S(2)O molecules are constructed using the configuration-based multireference second order perturbation theory and multireference configuration interaction with single and double excitations. Based on the PECs, the equilibrium structures of the ground state and several low-lying excited states, as well as the vertical and adiabatic transition energies, are obtained. Furthermore, avoided crossings and intersections displayed on the PECs are studied. The dissociation of states for the asymmetric bent S(2)O, especially the predissociative of the excited (~)C1A' state, is also discussed in detail. According to our calculations, the predissociation limit of (~)C1A' is found to be located in the vicinity of 2(6) or 2(5) (reckoning in the zero-point energy revision) S-S stretching vibration level, which is in good agreement with the available experimental data.