Yubin Wang

Detailed dynamics of the nonradiative deactivation of adenine: a semiclassical dynamics study.

A realistic dynamics simulation study is reported for the ultrafast radiationless deactivation of 9H-adenine. The simulation follows two different excitations induced by two 80 fs (fwhm) laser pulses that are different in energy: one has a photon energy of 5.0 eV, and the other has a photon energy of 4.8 eV. The simulation shows that the excited molecule decays to the electronic ground state from the (1)pipi* state in both excitations but through two different radiationless pathways: in the 5.0 eV excitation, the decay channel involves the out-of-plane vibration of the amino group, whereas in the 4.8 eV excitation, the decay strongly associates with the deformation of the pyrimidine at the C 2 atom. The lifetime of the (1) npi* state determined in the simulation study is 630 fs for the 5.0 eV excitation and 1120 fs for the 4.8 eV excitation. These are consistent with the experimental values of 750 and 1000 fs. We conclude that the experimentally observed difference in the lifetime of the (1) npi* state at various excitations results from the different radiationless deactivation pathways of the excited molecule to the electronic ground state.

Hole-particle correspondence in CI calculations

Abstract A new classification of spin-adapted MRCISD states using the hole–particle correspondence is given and formulas for the hole loop shapes are derived. Based on the classification and the formulas for hole loop shapes, an improved CI algorithm is suggested and coded. The new algorithm reduces disk storage requirement by over one hundred folds for an MRCISD calculation with 37 doubly occupied orbitals. Additionally, the code is very efficient. For a calculation of 10 7 CSFs, the average time per iteration is only 650 s on a PC.

On the interconversion pathway of HBO↔BOH

The potential energy surfaces have been constructed for the 1A, 3A, and 3A states of HBO by using the multireference perturbation theory with the basis set cc-pVTZ (6d,10f). Two stationary points and a transition state have been characterized on all the three surfaces, which are in good agreement with available experiments and previous calculations. The interconversion pathways from metastable boron hydroxide BOH to the considerably more stable HBO are expounded based on the nature of the surfaces.

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.

HIGH-LEVEL AB INITIO CALCULATION AND ASSESSMENT OF THE DISSOCIATION AND IONIZATION ENERGIES OF NH2 AND NH3 NEUTRALS OR CATIONS

Abstract QCISD(T) (full)/6–311 ++G(3df,3pd), QCISD(T) (full)/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ calculations are performed for some NH 2 and NH 3 neutrals and cations. Based on the calculations we assess the dissociation and ionization energies of these molecules reported earlier and point out that the large deviation between the previous dissociation energy of H 2 Nue5f8H + and ionization energy of NH 2 with those in other reports could be caused by too high a detected value of the proton appearance potential AP(H + ).

Explicit formulae for spin-dependent matrix elements in the unitary group approach

Abstract The matrix elements of spin-dependent U(2 n ) generators are given explicitly. These matrix elements are expressed in terms of those of spin-independent U( n ) and U( n +1) generators, and can therefore be easily incorporated into existing unitary group approach based programs.

An improved externally contracted CI method

Abstract An improved externally contracted CI algorithm is presented, aimed at reducing correlation energy loss and ensuring high efficiency. Some examples are tested by the new contracted CI method and improvements to various degrees with respect to original externally contracted CI are shown. Moreover, a new definition of the `canonical order for integrals is suggested which seems to be more efficient and general for addressing integrals with two or more indices.

An adjustable contracted CI method

A new contracted CI scheme—adjustable contracted CI scheme—is presented and programed. The efficiency of this scheme is tested by some example calculations. The result shows that the application of the new scheme is flexible and the correlation energy loss is lower than that of the original externally contracted CI method. Keywords: configuration interaction, contracted CI method, correlation energy.

SEVERAL EXCITED STATES AND THERMOCHEMICAL PROPERTIES OF PHN (N = 1-3) : A HIGH LEVEL AB INITIO STUDY

Abstract Comparative ab initio calculations at QCISD(T), CCSD(T) and MRCISD levels of theory with four large basis sets were performed on neutrals and some cations of the PHn (n=1–3) species. Some of dissociation and ionization reactions and excited states related to these species were discussed and the results were compared with those of experiments and the earlier theoretical calculations.