In this paper,we examined the performance of 12 density functionals(B3LYP,X3LYP,O3LYP,PBE0,B3PW91,BLYP,OLYP,OPBE,PBE,BPW91,VSXC and TPSS),combined with two basis sets[DZP++ and 6-311+G(3df,2p)] in the prediction of the adiabatic electron affinities against a set of 91 well-established experimental values.We have reached a conclusion that all these modern functionals are ge-nerally good,giving a mean absolute deviation(MAD)less than 0.24 eV.B3LYP and X3LYP are among the most reliable methods for this test set.When the DZP++ basis set is adopted,X3LYP is the best with a MAD of 0.14 eV,while B3LYP leads to a MAD of 0.16 eV.When the basis set is extended to 6-311+G(3df,2p),B3LYP improves its MAD to 0.13 eV,while the MAD of X3LYP remains to be 0.14 eV.Most hybrid functionals outperform the corresponding GGA functinals,with the exception of PBE0.The meta-GGA functionals(VSXC and TPSS)are not necessarily better than the GGA functionals.Our calculations also reveal that there are flaws associated with the OPTX exchange functional in the calculations of EA.
FeAs^- single layer is tested as a simple model for LaFeAsO and BaFe2As2 based on firstprinciples calculations using generalized gradient approximation （GGA） and GGA＋U. The calculated single-layer geometric and electronic structures are inconsistent with that of bulk materials. The bulk collinear antiferromagnetic ground state failed to be obtained in the FeAs^- single layer. The monotonous behavior of the Fe-As distance in z direction upon electron or hole doping is also in contrast with bulk materials. The results indicate that, in LaFeAsO and BaFe2As2, interactions between FeAs layer and other layers beyond simple charge doping are important, and a single FeAs layer may not represent a good model for Fe based superconducting materials.
Diblock oligomers are widely used in molecular electronics. Based on fully self-consistent nonequilib-rium Green's function method and density functional theory, we study the electron transport properties of the molecular junction with a dipyrimidinyl-diphenyl (PMPH) diblock molecule sandwiched between two gold electrodes. Effects of different kinds of molecule-electrode anchoring geometry and protona-tion of the PMPH molecule are studied. Protonation leads to both conductance and rectification en-hancements. However, the experimentally observed rectifying direction inversion is not found in our calculation. The preferential current direction is always from the pyrimidinyl to the phenyl side. Our calculations indicate that the protonation of the molecular wire is not the only reason of the rectification inversion.
With density functional theory, the mechanism of water-enhanced CO oxidation on oxygen pre-covered Au (111) surface is theoretically studied. First, water is activated by the pre-covered oxygen atom and dissociates to OHads group. Then, OHads reacts with COads to form chemisorbed HOCOads. Finally, with the aid of water, HOCOads dissociates to CO2. The whole process can be described as 1/2H2Oads + H2Oads + 1/2Oads+ COads→H3Oads + CO2, gas. One CO2 is formed with only 1/2 pre-covered oxygen atom. That is why more CO2 is observed when water is present on oxygen pre-covered Au (111) surface. Activation energy of each elementary step is low enough to allow the reaction to proceed at low temperature.
We present a systematic study of 1:1 glycine-water complexes involving all possible glycine conformers. The complex geometries are fully optimized for the first time both in the gas phase and in solution using three DFT methods (B3LYP, PBE1PBE, X3LYP) and the MP2 method. We calculate the G3 energies and use them as the reference data to gauge hydrogen bond strength in the gas phase. The solvent effects are treated via the integral equation formalism-polarizable continuum model (IEF-PCM). Altogether, we locate fifty-two unique nonionized (N) structures and six zwitterionic (Z) structures in the gas phase, and fifty-five N structures and thirteen Z structures in solution. Both correlation and solvation are shown to be important in geometry determination. We found that in the gas phase, a water molecule binds more strongly to the carboxylic acid group of glycine than to its amine group, whereas in solution phase the reverse is true. The most stable Z structure is isoenergetic with the most stable N structure.
