Liqun Deng

A combined density functional and intrinsic reaction coordinate study on the ground state energy surface of H2CO

Approximate density functional theory (DFT) has been used to study four elementary processes on the singlet ground state energy surface of H2CO. The elementary steps include the elimination of H2 and CO from formaldehyde, the transformation of formaldehyde to trans‐hydroxymethylene, the isomerization of trans‐hydroxymethylene to cis‐hydroxymethylene, and the 1,2 elimination of H2 from cis‐hydroxymethylene. The DFT studies were based on the local density approximation (LDA) as well as a nonlocal self‐consistent field (NL‐SCF) extension in which Perdew’s correlation correction and Becke’s exchange correction were added to LDA. Fully optimized structures as well as harmonic vibrational frequencies have been evaluated for all of the stationary points corresponding to the reactants, products, and transition states for the four reactions within the LDA and NL‐SCF approximations. The four reactions have in addition been studied by the intrinsic reaction coordinate (IRC) method in which stationary points on the p...

Towards more realistic computational modeling of homogenous catalysis by density functional theory: combined QM/MM and ab initio molecular dynamics

Abstract The combined quantum mechanics/molecular mechanics (QM/MM) and the ab initio molecular dynamics methods (AIMD) are fast emerging as viable computational molecular modeling tools. Both methods allow for the incorporation of effects that are often ignored in high level calculations, but may be critical to the real chemistry of the simulated system. In the combined QM/MM method part of the system, say the active site, is treated quantum mechanically whereas the remainder of the system is treated with a faster molecular mechanics force field. This allows high level calculations to be performed where the effects of the environment are incorporated in a computationally tractable manner. With the ab initio molecular dynamics methods, the system is simulated at a finite temperature with no empirical force field. Rather, the forces at each time step are determined with a full electronic structure calculation at the density functional level. Thus, simulations of chemical reactions can be performed where finite temperature effects are realistically represented. In this paper a brief introduction to both methods is given. The methods are further demonstrated with specific applications to modeling homogenous catalytic processes at the molecular level. These applications are our latest efforts to build more realistic computational models of catalytic systems at the density functional level.

General aspects of ethylene polymerization by d0 and d0f n transition metals

We present a generalized view of d0and d0fn metal complexes as olefin polymerization catalysts from computational studies of the {L}M–C2H5(0,+,2+)-fragments (M = Sc(III), Y(III), La(III), Lu(III), Ti(IV), Zr(IV), Hf(IV), Ce(IV), Th(IV) and V(V); L = NH–(CH)2–NH2- {1}, N(BH2)–(CH)2–(BH2)N2- {2}, O–(CH)3–O- {3}, Cp22- {4}, NH–Si(H2)–C5H42- {5}, {(oxo)(O–(CH)3–O)}3- {6}, (NH2)22- {7}, (OH)22- {8}, (CH3)22- {9}, NH–(CH2)3–NH2- {10} and O–(CH2)3–O2- {11}).