A new direct ab initio dynamics method for calculating thermal rate constants from density functional theory

Abstract

We present a new direct ab initio dynamics methodology for calculating thermal rate constants from density functional theory (DFT). Dynamical theory is based on a full variational transition state theory plus multidimensional semiclassical tunneling approximations. We have applied this approach to the CH3+H2→CH4+H abstraction reaction using the BH&H-LYP method which is the combination of the hybrid Becke’s half-and-half (BH&H) method for nonlocal exchange and Lee–Yang–Parr (LYP) functional for nonlocal correlation. The 6-311G(d,p) basis set was used in these calculations. To obtain quantitative results, the classical potential energy along the minimum energy path (MEP) was corrected either by scaling to match a more accurate ab initio results for the barrier heights or by carrying out single point calculations at selected points along the MEP at a more accurate level of ab initio molecular orbital (MO) theory. By comparing with our previous QCISD results and experimental rate constants, we found that DFT particular the BH&H-LYP method can provide sufficient accurate potential energy surface information for rate calculations for this system. The present direct DFT dynamics method can be used for reactive dynamics studies of reactions involving large polyatomic molecules from first principles. More work however is still needed to test the accuracy of DFT methods for such calculations.

Parametrized direct dynamics study of rate constants of H with CH4 from 250 to 2400 K

“…In the present paper, we will present dynamics calculations based on a parametrized MPWX surface, which agrees well with a presumed-reliable experimental measurement 10 for reaction ͑1͒. Another hybrid density function method called BH&HLYP has been used in previous work 31 for rate calculations for reaction ͑1͒. BH&HLYP is similar to MPW1K but uses different gradientcorrection functionals and sets the percentage of HF exchange to 50%.…”

Using complex degrees of freedom in the Kohn-Sham self-interaction correction

“…However, DFT using local or semilocal density functionals is also well known for some notorious failures : wrong prediction of dissociation limits [6,7] and chemical reaction barriers [8,9], as well as missing Rydberg series and instability of anions [10,11]. Standard functionals tend to overestimate charge-transfer properties, as, for example, polarizabilities of molecular chains [12,13,[24][25][26][27] and charge transport in molecular devices [14][15][16].…”

Kinetics of the hydrogen abstraction ROH + H → RO• + H2 reaction class

“…A hybrid nonlocal DFT, particularly Becke's half-and-half [26] (BH&H) nonlocal exchange, and Lee-Yang-Parr [27] (LYP) nonlocal correlation functionals, has been found previously to be sufficiently accurate for predicting the transition state properties of hydrogen abstraction reactions [28,29]. Note that within the RC-TST framework, as discussed above, only the relative barrier heights are needed.…”