Hong-Gang Fu

First-principles calculations of the stability and electronic properties of the PbTiO3 (110) polar surface

The structural and electronic properties of five terminations of cubic lead titanate (PbTiO3) (110) polar surface were investigated by first‐principles total‐energy calculations using a periodic slab model. On the PbTiO termination, an anomalous filling of conduction band was observed, whereas on the O2 termination, two surface oxygen atoms formed a peroxo group, demonstrating that the electronic structures of the two stoichiometric terminations undergo significant changes with respect to bulk materials. However, for the three nonstoichiometric TiO‐, Pb‐, and O‐terminated surfaces, their electronic structures are very similar to bulk. Charge redistribution results for the five terminations confirmed that electronic structure and surface composition changes are responsible for their polarity compensation. However, which mechanism actually dominates the stabilization process depends upon energetic considerations. A thermodynamic stability diagram suggested that the two stoichiometric terminations are unstable; however, the three nonstoichiometric terminations can be stabilized in some given regions. Furthermore, this study indicates that the very different stabilities and surface states filling behaviors of the PbTiO3 (110) polar surface with respect to SrTiO3 and BaTiO3 ones seem to originate from the partially covalent characteristics of Pbuf8ffO pairs.

Computational study on structures, isomerization and dissociation of [Si, N, C, O]+ isomers

Abstract A detailed singlet potential energy surface (PES) of the [Si, N, C, O]+ system including 13 isomers and 15 transition states is investigated by means of the MP2 and QCISD(T) (single-point) methods. At the final QCISD(T)/6-311+G(3df)//MP2/6-311G(d) level with zero-point energy inclusion, SiNCO+ 1 is found to be thermodynamically the most stable isomer followed by SiOCN+ 2, OSiCN+ 3, OSiNC+ 4 and SiCNO+ 5 at 40.90, 70.00, 70.43 and 87.72xa0kcalxa0mol−1, respectively. For isomer 1, the isomerization to the species, 2, 3 and 4 can very favorably compete with its direct dissociation, and thus, together with the structural and bonding analysis, the very recent mass spectrometric experiment can reasonably be interpreted. Furthermore, our results indicate that while 1 is kinetically the most stable, the species, 3, 4 and 5 are also shown to reside in very deep potential wells. Therefore, in addition to the mass spectroscopically characterized isomers 1 and 3, the species 4 and 5 should also be experimentally observable. However, observation of the second low-lying isomer 2 seems less likely due to its easy conversion to isomer 1 via a four-membered ring Si-shift process.

Combined DFT, QCISD(T), and G2 mechanism investigation for the reactions of carbon monophosphide CP with unsaturated hydrocarbons allene CH2CCH2 and methylacetylene CH3CCH

The possible reaction product distribution and mechanism of carbon monophosphide CP with unsaturated hydrocarbons allene CH2CCH2 and methylacetylene CH3CCH are investigated at the B3LYP/6‐311+G(d,p), QCISD(T)/6‐311++G(2df,2p), and G2 levels of theory. Corresponding reactants, products, intermediates, and interconversion and dissociation transition states are located on the reaction potential energy profiles. Computation results show that in the reaction of CP with CH2CCH2 the dominant reaction product should be species CH2CCHCP. Also, we can suggest species HCCCH2CP as a secondary reaction product despite of only minor contribution to reaction products. In the reaction of CP with CH3CCH, the primary and secondary products are suggested to be two important molecules HCCCP and CH3CCCP, respectively. The predicted mechanisms for the two reactions are not in parallel with the reactions of CN with allene CH2CCH2 and methylacetylene CH3CCH given in previous studies. The present calculations provide some useful information for future possible experimental isolation and observation for some interesting unsaturated carbon–phosphorus‐bearing species.

Theoretical investigation on the protonation reactions and products of the stable [N,C,C,S] isomers

A theoretical study on the protonation system of [N,C,C,S], [H,N,C,C,S]+, was performed at the B3LYP/6‐311++G(d,p) and CCSD(T)/6‐311++G(2df,2p) (single point) levels of theory. On the doublet [H,N,C,C,S]+ surface, 24 species were located as energy minima and 10 of them were considered as kinetically stable species. The species HNCCS+ with 2A′ state and a shallow W‐shaped skeleton was predicted to be the global minimum and kinetically the most stable species, being in good agreement with previous experimental findings. Furthermore, the protonation reactions of the stable [N,C,C,S] isomers were investigated in detail. The calculation results indicated that the [N,C,C,S] isomers may be significantly stabilized upon protonation. Finally, the possible covalent structures of the [H,N,C,C,S]+ isomers with considerable stability were briefly discussed.