The present work assessed several exchange-correlation functionals (including GGA, meta-GGA and hybrid functionals), in combination with a variety of basis sets and effective core potentials (ECP) for their ability to predict the ground spin state of Mn(III) meso-tetraphenylporphyrin chloride complex, labeled Mn(III)TPPCl, for which experimental data support the quintet high spin state. Geometry optimization of Mn(III)TPPCl was performed for three possible spin states (singlet state, LS; triplet state, IS; and quintet state, HS) at the TPSSh level using the LANL2DZ ECP for Mn and the 6-311G(d) basis set for C, N, Cl and H. Afterwards, single-point energy calculations were conducted by applying 18 exchange-correlation functionals (BLYP, B3LYP, PW91, BPW91, BP86, OLYP, OPBE, OPW91, O3LYP, PBE0, PBEh1PBE, HSEH1PBE, TPSS, TPSSh, M06 L, M06, M062X and M06HF). The influence of the basis set for the metal center was assessed using a smaller group of functionals and varying between the Pople basis set 6-31G(d), its newer formulation m6-31G(d) and the larger Def2-QZVP basis set. All functionals in combination with Pople basis sets predict the quintet state as the ground spin state. In addition, the BLYP, BP86, BPW91, PW91, PBEh1PBE, TPSS and TPSSh functionals predicted the IS lying at most ~60 kJ mol?1 above the HS, which agrees with the reference data. Results including Def2-QZVP basis set were inconsistent, since only BLYP and B3LYP predict HS as the ground spin state. The recommended methodology for the treatment of such systems seems to be exchange-correlations functionals with few or none Hartree-Fock exchange and modest size basis sets.
The electronic structures and spectroscopic properties of two complexes [M(pic)3] (M = Ir, Rh) containing picolinate as bidentate ligands have been calculated by means density functional theory (DFT) and time-dependent DFT/TD-DFT using three hybrid functionals B3LYP, PBE0 and mPW1PW91. The PBE0 and mPW1PW91 functionals, which have the same HF exchange fraction (25%), give similar results and do not differ drastically from B3LYP results. Calculated geometric parameters of the complexes are in good agreement with the available experimental data. The UV absorptions observed in acetonitrile were assigned on the basis of singlet state transitions. The most intense band observed in the UV-C region corresponds to ligand-to-ligand charge transfer states (LLCT) in both complexes. The theoretical spectrum of the rhodium complex is characterized by a large degree of mixing between metal-to-ligand-charge-transfer (MLCT), LLCT and metal centered (MC) states in the UV-A region. The presence of low-lying excited states with MC character affects the absorption spectrum under spin-orbit coupling (SOC) effects and play important roles in the photochemical properties.
Performance of 18 DFT functionals (B1B95, B3LYP, B3PW91, B97D, BHandHLYP, BMK, CAM-B3LYP, HSEh1PBE, M06-L, mPW1PW91, O3LYP, OLYP, OPBE, PBE1PBE, tHCTHhyb, TPSSh, wB97xD, VSXC) in combinations with six basis sets (cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, aug-cc-pVTZ, IGLO-II, and IGLO-III) and three methods for calculating magnetic shieldings (GIAO, CSGT, IGAIM) was tested for predicting 1H and 13C chemical shifts for 25 organic compounds, for altogether 86 H and 88 C atoms. Proton shifts varied between 1.03 ppm to 12.00 ppm and carbon shifts between 7.87 ppm to 209.28 ppm. It was found that the best method for calculating 13C shifts is PBE1PBE/aug-cc-pVDZ with CSGT or IGAIM approaches (mae?=?1.66 ppm), for 1H the best results were obtained with HSEh1PBE, mPW1PW91, PBE1PBE, CAM-B3LYP, and B3PW91 functionals with cc-pVTZ basis set and with CSGT or IGAIM approaches (mae?=?0.28 ppm). We found that often larger basis sets do not give better results for chemical shifts. The best basis sets for calculating 1H and 13C chemical shifts were cc-pVTZ and aug-cc-pVDZ, respectively. CSGT and IGAIM NMR approaches can perform really well and are in most cases better than popular GIAO approach.
Graphical Abstract Mean absolute errors for 1H and 13C chemical shifts and computational times of neutral toluene molecule with aug-cc-pVDZ basis set and CSGT approach
Hydroxyquinolone derivatives have proven to be useful for inhibition at the glycine binding site of N-methyl-D-aspartate (NMDA)
receptor. In this work the electronic structure, molecular electrostatic potential (MESP) and vibrational characteristics
of a set of C3 substituted 4-hydroxyquino-2-lone (HQ) derivatives, which act as Glycine/NMDA receptor antagonists, have been investigated
using the density functional calculations. In the optimized structures a substituent at the C3 site of HQ tends to adopt a helical structure. MESP investigations reveal that the ligands showing better inhibition activity
should possess electron-rich regions extending over the substituent and carbonyl group of HQ. A correlation of inhibitory
activity to the molecular electrostatic potential topography at the carbonyl oxygen as well as to the molecular electron density
topography turns out to be a significant output of the investigation.
Figure Quantam chemical approach has been employed to understand the reactivity of a set of hydroxyquinolone derivatives known for
their inhibition activity towards Glycine/NMDA receptor. Molecular electrostatic potential topography has been used as a tool
to understand the reactivity pattern 相似文献
The UV-Vis spectra of series of polymethylmethacrylate (PMMA) copolymers with attached trans-azobenzene derivatives were measured
in 1,1,2-trichloroethane. In order to gain some insight into the recorded spectra, the quantum chemical calculations were
performed for the substituted azobenzenes using both configuration interaction with single excitations method (CIS) as well
as density functional theory (DFT) with B3LYP and PBE0 functionals. The calculations were performed in solvent. In particular,
we found that the PBE0 excitation energies are in very good agreement with the experimental data.
Figure The plots of orbital contour surfaces for molecule II. The molecular orbitals were calculated at the PBE0/6-311++G(d,p) level of theory. The upper plot presents contour surface of HOMO and the lower presents contour surface of LUMO. Shown are the contour surfaces of orbital amplitude 0.04 (red) and -0.04 (blue) 相似文献
In some halides RX, the halogen X has a region of positive electrostatic potential on its outermost portion, centered around
the extension of the R−X bond. The electrostatic attraction between this positive region and a lone pair of a Lewis base is
termed halogen bonding. The existence and magnitudes of such positive potentials on some covalently bonded halogens, and the
characteristic directionality of the interaction, can be explained in terms of the degree of sp hybridization and polarizability of X and the electronegativity of R. Halogen bonding increases in strength in the order
Cl < Br < I; fluorine is frequently said to not form halogen bonds, although a notable result of the present study is computational
evidence that it does have the capability of doing so, if R is sufficiently electron withdrawing. An increasingly important
application of halogen bonding is in the design of new materials (e.g., crystal engineering). In this paper, we present the
calculated energies of a series of halogen-bonding interactions that could be the basis for forming linear chains, of types
X----X----X---- or X----Y----X----Y----. We focus upon chlorides and bromides, and nitrogen bases. The B3PW91/6-311G(3df,2p)
and MP2/6-311++G(3df,2p) procedures were used. We show how the computed electrostatic potentials (B3PW91/6-31G**) can provide
guidance in selecting appropriate halide/base pairs.
Figure Computed electrostatic potential of CH3CH2Br on the molecular surface defined by the 0.001-au contour of the electronic density. The bromine is facing the reader, and
has a small positive (green) region centered around the intersection of the C–Br axis with the surface 相似文献
We have carried out B3PW91 and MP2-FC computational studies of dimethyl sulfoxide, (CH3)2SO, and dimethyl sulfone, (CH3)2SO2. The objective was to establish quantitatively the basis for their high polarities and boiling points, and their strong solvent
powers for a variety of solutes. Natural bond order analyses show that the sulfur–oxygen linkages are not double bonds, as
widely believed, but rather are coordinate covalent single S+→O− bonds. The calculated electrostatic potentials on the molecular surfaces reveal several strongly positive and negative sites
(the former including σ-holes on the sulfurs) through which a variety of simultaneous intermolecular electrostatic interactions
can occur. A series of examples is given. In terms of these features the striking properties of dimethyl sulfoxide and dimethyl
sulfone, their large dipole moments and dielectric constants, their high boiling points and why they are such good solvents,
can readily be understood.
Figure Dimers of dimethyl sulfoxide (DMSO; left) and dimethyl sulfone (DMSO2; right) showing O S—O -hole bonding and C H—O hydrogen bonding. Sulfur atoms are yellow, oxygens are red, carbons are gray and hydrogens are white相似文献
The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation
on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density
functional method at the 6-31G** basis set level. The barrier heights for H2O-assisted reactions are significantly lower than that of unassisted tautomerization reaction in the gas phase. Nonspecific
solvent effects have also been taken into account by using the continuum model (IPCM) of four different solvent. The tautomerization
energies and the potential energy barriers are decreased by increasing solvent polarity.
Figure The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation
on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density
functional method at the 6-31G** basis set level 相似文献
Realistic molecular models of one and two-centre catalytic active sites originating from the cleavage of a precursor material
known to give rise to an active double metal cyanide catalyst are described. Via periodic density functional calculations
the structure of the proposed catalytic sites are shown to be dependent on electrostatic and structural relaxation processes
occurring at the surfaces of the precursor material. It is shown how these effects may be adequately captured by small molecular
models of the active sites. The general methodology proposed should provide a computationally efficient basis for detailed
future studies into catalytic reactions over double metal cyanide materials.
Figure Reconstructed DMC [100]-surface: electrostatic potential mapped on charge density isosurface
This work has been originally presented on the Modelling and Design of Molecular Materials conference in Wrocław, Poland. 相似文献
The effect of microsolvation on zwitterionic glycine, considering both (-NH3(+)) as proton donor and (-COO(-)) as proton acceptor at correlated ab initio (MP2) level and density functional methods (B3LYP, PW91, MPW1PW91 and PBE) using 6-311++G** basis set has been reported. DFT methods have been employed so as to compare the performance/quality of different gradient-corrected correlation functionals (PW91, PBE), hybrid functionals (B3LYP, MPW1PW91) and to predict the near quantitative structural and vibrational properties, at reduced computational cost. B3LYP method outperforms among the different DFT methods for the computed hydrogen bond distances and found closer to the value obtained by correlated MP2 level, whereas MPW1PW91 and PBE methods shows very similar values but approximately 0.03 A less, compared to B3LYP method. MP2 calculation and single point CCSD(T)//MP2 calculation have been considered to decompose the interaction energy, including corrections for basis set superposition error (BSSE). Moreover, charge distribution analysis has also been carried out to understand the long raised questions, how and why the two body energies have significant contribution to the total binding energy. 相似文献
A theoretical study of a sandwich compound with a metal monolayer sheet between two aromatic ligands is presented. A full
geometry optimization of the [Au3Cl3Tr2]2+ (1) compound, which is a triangular gold(I) monolayer sheet capped by chlorines and bounded to two cycloheptatrienyl (Tr)
ligands was carried out using perturbation theory at the MP2 computational level and DFT. Compound (1) is in agreement with
the 18–electron rule, the bonding nature in the complex may be interpreted from the donation interaction coming from the Tr
rings to the Au array, and from the back-donation from the latter to the former. NICS calculations show a strong aromatic
character in the gold monolayer sheet and Tr ligands; calculations done with HOMA, also report the same aromatic behavior
on the cycloheptatrienyl fragments giving us an insight on the stability of (1). The Au –Au bond lengths indicate that an
intramolecular aurophilic interaction among the Au(I) cations plays an important role in the bonding of the central metal
sheet.
Figure (a) Ground state geometry of complex 1; (b) Top view of compound 1 and Wiberg bond orders computed with the MP2/B1 computational method; (c) Lateral view of compound 1 and NICS values calculated with the MP2/B1 method; the values in parenthesis were obtained at the VWN/TZP level 相似文献
The productive self-metathesis reaction of 1-octene in the presence of the Phobcat precatalyst [RuCl2(Phoban-Cy)2(=CHPh)] using density functional theory was investigated and compared to the Grubbs 1 precatalyst [RuCl2(PCy3)2(=CHPh)]. At the GGA-PW91/DNP level, the geometry optimization of all the participating species and the PES scans of the various
activation and catalytic cycles in the dissociative mechanism were performed. The formation of the catalytically active heptylidene
species is kinetically and thermodynamically favored, while the formation of trans-tetradecene is thermodynamically favored.
相似文献
It has been observed both experimentally and computationally that some divalently-bonded Group VI atoms interact in a noncovalent
but highly directional manner with nucleophiles. We show that this can readily be explained in terms of regions of positive
electrostatic potential on the outer surfaces of such atoms, these regions being located along the extensions of their existing
covalent bonds. These positive regions can interact attractively with the lone pairs of nucleophiles. The existence of such
a positive region is attributed to the presence of a “σ-hole.” This term designates the electron-deficient outer lobe of a
half-filled p bonding orbital on the Group VI atom. The positive regions become stronger as the electronegativity of the atom decreases
and its polarizability increases, and as the groups to which it is covalently bonded become more electron-withdrawing. We
demonstrate computationally that the σ-hole concept and the outer regions of positive electrostatic potential account for
the existence, directionalities and strengths of the observed noncovalent interactions.
Figure Calculated B3PW91/6-31G** electrostatic potential of F2S, computed on the 0.001 electrons/bohr3 contour of the electronic density. The sulfur atom is toward the reader; the red areas indicate the most positive potentials,
reaching +34.4 kcal/mole, along the extensions of the F-S bonds. The purple region (negative) on the left and the one (not
totally visible) on the right side of the sulfur are due to its nonbonded s and p electrons. The fluorines (top left and bottom left) also have negative regions of potential (purple areas) 相似文献
Eight H-bonded complexes between serotonin (5-hydroxy-tryptamine) and water/hydrogen peroxide were studied at the B3LYP and
HF levels of theory, using the 6-31+G(d) basis set. A thermodynamic analysis was performed in order to find the most stable
complex. The calculated bonding parameters showed that the most stable H-bonded complex is formed between serotonin and hydrogen
peroxide by means of the intermolecular H-bond –H2N...H–OOH.
Fig. a Theoretical study of the hydrogen-bonded supersystems serotonin-water/hydrogen peroxide 相似文献
The equilibrium geometries and electron affinities of the R-SS/R-SS-(R=CH3, C2H5, n-C3H7, i-C3H7, n-C4H9, t-C4H9, n-C5H11) species have been studied using the higher level of the Gaussian-3(G3) theory and 21 carefully calibrated pure and hybrid density functionals (five generalized gradient approximation (GGA) methods, seven hybrid GGAs, three meta GGA methods, and six hybrid meta GGAs) in conjunction with diffuse function augmented double-ζ plus polarization (DZP++) basis sets. The geometries are fully optimized with each method and discussed. The reliable adiabatic electron affinity has been presented by means of the high level of G3 technique. With the DZP++ DFT method, three measures of neutral/anion energy differences reported in this work are the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy. The adiabatic electron affinities, obtained at the BP86, M05-2X, B3LYP, M06, B98, M06-2X, mPW1PW91, HCTH, B97-1, M05, PBE1PBE, and VSXC methods, are in agreement with the G3 results. These methods perform better for EA prediction and are considered to be reliable. 相似文献
The mechanism of the enantioselective deprotonation of cyclohexene oxide with isopinocampheyl-based chiral lithium amide was studied by quantum chemical calculations. The transition states of eight molecules were fully optimized at the ab initio HF/3-21G and density functional B3LYP/3-21G levels with Gaussian 98. The activation energies were calculated at the B3LYP/6-31+G(3df,2p)//B3LYP/3-21G level. We found the theoretical evaluation to be consistent with the experimental data. At the best case, an enantiomeric excess of up to 95% for (R)-2-scyclohexen-1-ol was achieved with (−)-N, N-diisopinocampheyl lithium amide.
Enantioselective deprotonation of cyclohexene oxide
Electronic Supplementary Material Supplementary material is available for this article at
Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday. 相似文献
Effects of size, shape, and pyrene doping on electronic properties of graphene nanoflakes (GNFs) were theoretically investigated using density functional theory method with PBE, B3PW91, and M06-2X functionals and cc-pVDZ basis set. Two shapes of zigzag GNFs, hexagonal (HGN) and rhomboidal (RGN), were considered. The energy band gap of GNF depends on shape and decreases with size. The HGN has larger band gap energy (1.23–3.96 eV) than the RGN (0.13–2.12 eV). The doping of pyrene and pyrene derivatives on both HGN and RGN was also studied. The adsorption energy of pyrene and pyrene derivatives on GNF does not depend on the shape of GNFs with energies between 21 and 27 kcal mol?1. The substituent on pyrene enhances the binding to GNF but the strength does not depend on electron withdrawing or donating capability. The doping by pyrene and pyrene derivatives also shifts the HOMO and LUMO energies of GNFs. Both positive (destabilizing) and negative (stabilizing) shifts on HOMO and LUMO of GNFs were seen. The direction and magnitude of the shift do not follow the electron withdrawing and donating capability of pyrene substituents. However, only a slight shift was observed for doped RGN. A shift of 0.19 eV was noticed for HOMO of HGN doped with 1-aminopyrene (pyNH2) and of 0.04 eV for LUMO of HGN doped with 1-pyrenecarboxylic acid (pyCOOH).
We have evaluated the performance of 15 density functionals of diverse complexity on the geometry optimization and energetic evaluation of model reaction steps present in the proposed reaction mechanisms of Cu(I)-catalyzed indole synthesis and click chemistry of iodoalkynes and azides. The relative effect of the Cu+ ligand on the relative strength of Cu+-alkyne interactions, and the strong preference for a π-bonding mode is captured by all functionals. The best energetic correlations with MP2 are obtained with PBE0, M06-L, and PBE1PW91, which also provide good quality geometries. Furthermore, PBE0 and PBE1PW91 afford the best agreement with the high-level CCSD(T) computations of the deprotonation energies of Cu+-coordinated eneamines, where MP2 strongly disagrees with CCSD(T) and the examined DFT functionals. PBE0 also emerged as the most suitable functional for the study of the energetics and geometries of Cu+ hydrides, while at the same time correctly capturing the influence of the Cu+ ligands on the metal reactivity. 相似文献
The three-dimensional (3D) structure of the catalytic domain of Gas1p, a protein belonging to the only family of β-(1,3)-glucan
transferases so far identified in yeasts and some pathogenic fungi (family GH-72), has been predicted by combining results
derived from threading methods, multiple sequence alignments and secondary-structure predictions. The 3D model has allowed
the identification of several residues that are predicted to play a crucial role in structural integrity, substrate recognition
and catalysis. In particular, the model of the catalytic domain can be useful for designing site-directed mutagenesis experiments
and for developing inhibitors of Gas1p enzymatic activity.
Figure Three-dimensional models of the Gas1p catalytic domain as predicted using as template 7A3H (PDB code) protein
Electronic Supplementary Material Supplementary material is available for this article at 相似文献