Electron Correlation Corrections Research Articles

An ab initio study of M 2Te (M=Cu,Ag,Au) systems

The equilibrium geometries and the vibrational frequencies of M 2Te (M=Cu,Ag,Au) systems were calculated at HF, second- to fourth-order Møller–Plesset perturbation theory (MP2, MP3, MP4), and coupled cluster methods (CCSD, CCSD(T)) levels, and using relativistic and non-relativistic pseudopotentials for Au 2Te. The calculated geometries indicated that the species has a bent structure of about 70° angle. Electron correlation corrections on the bond angle are very significant, in general, angles M–Te–M are reduced from 90° to 70°, and on the bond length are small. The property of the electron correlation is analyzed, it seems to be explained in terms of a tangential force. Relativistic effects significantly shorten the bond length of Au 2Te. Comparing Au 2Te with Cu 2Te and Ag 2Te, it could be predicted that the Au 2Te is relatively stable.

First-principles calculations of perovskite thin films

The results of the electronic structure calculations for different surface terminations of SrTiO 3 (1 0 0) perovskite thin films are discussed. These calculations are based on ab initio Hartree–Fock method with a posteriori electron correlation corrections and density functional theory with a number of different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Results are compared with previous ab initio plane-wave local density approximation and classical shell model calculations. Calculated considerable increase of the Ti–O chemical bond covalency nearby the surface is confirmed by experimental data. We predict also the band-gap reduction, especially for TiO 2 termination.

High Level ab Initio Calculations of Intermolecular Interaction of Propane Dimer: Orientation Dependence of Interaction Energy

Intermolecular interaction of the propane dimer was calculated with the MP2 level electron correlation correction using several basis sets up to the cc-pVQZ. The calculated interaction energy greatly depends on the basis set. Small basis sets underestimate the attraction considerably. The effects of electron correlation beyond MP2 are not large. Intermolecular interaction energies of 23 orientations of propane dimers were calculated at the MP2 level with a large basis set including multiple polarization functions. In all dimers, the inclusion of electron correlation considerably increases the attraction. The dispersion interaction is found to be the major source of attraction, whereas the electrostatic interaction is very small. The C2h dimer in which the two C2 axes of propane monomers have antiparallel orientation has the largest binding energy. The separation between the two methylene carbon atoms at the potential minimum in this dimer is the shortest among the 23 dimers. The short separation, which increases the dispersion energy, is the cause of the large binding energy of the C2h dimer. The estimated MP2 and CCSD(T) interaction energies of the propane dimer at the basis set limit are −1.99 and −1.94 kcal/mol, respectively.

Effect of electron correlation corrections on phase competition in Ag film on MgO substrate

The effect of electron correlation corrections in the novel theory predicting the growth mode of a thin metallic film on an insulating substrate has been studied. We discuss the influence of the substrate slab thickness on the energies of formation for several two-dimensional phases, which, in principle, may form in Ag layer on (001) MgO substrate. We analyze also the sensitivity of the key energy parameter––Fourier transform of the mixing potential V(0) to the choice of correlation functionals.

Magnitude and orientation dependence of intermolecular interaction between perfluoroalkanes: High level ab initio calculations of CF4 and C2F6 dimers

Intermolecular interaction energies of eight orientation CF4 dimers and seven orientation C2F6 dimers were calculated with electron correlation correction by the second-order Møller–Plesset perturbation (MP2) method. The D3d CF4 dimer and C2h C2F6 dimer have the largest binding energies. Electron correlation correction increases the attraction considerably, while the effects of electron correlation beyond MP2 are small. Electrostatic and induction energies are not large in all cases. This indicates that dispersion interaction is mainly responsible for the attraction. The calculated binding energy of the CF4 dimer (0.69 kcal/mol) is about 60% larger than that of the CH4 dimer (0.44 kcal/mol), while the binding energy of the C2F6 dimer (1.02 kcal/mol) is close to that of the C2H6 dimer (0.90 kcal/mol). The intermolecular separations (C⋯C distance) in the CF4 and CH4 dimers at the potential minima are close (4.0 and 3.8 Å, respectively), while the separation in the C2F6 dimer (4.8 Å) is appreciably larger than that in the C2H6 dimer (4.0 Å). The larger intermolecular separation in the C2F6 dimer reduces dispersion energy. Therefore the binding energies of the C2F6 and C2H6 dimers are not largely different. The molar volume of C2F6 is substantially larger than that of C2H6 due to bulky fluorine atoms. The small difference of the binding energies suggests that the large molecular volume of perfluoroalkanes is the cause of their small heats of vaporization per volume.

Electric quadrupole and hexadecapole moments for X2CCX2, X = H, F, Cl, Br, and I*

AbstractWe have calculated electric quadrupole and hexadecapole moments for ethene, tetrafluoroethene, tetrachloroethene, tetrabromoethene, and tetraiodoethene. A large basis set of [9s6p5d2f/5s4p2d] size is thought to provide reference near‐Hartree–Fock results for the electric multipole moments of ethene: Θxx=1.34 and \documentclass{article}\pagestyle{empty}\begin{document}$\Theta_{zz}=1.53\ ea_{0}^{2}$\end{document} for the quadrupole Φxxxx=−17.38, Φyyyy=20.29, and \documentclass{article}\pagestyle{empty}\begin{document}$\Phi_{zzzz}=-17.04\ ea_{0}^{4}$\end{document} for the hexadecapole moment (with z as the CC axis and the molecule on the xz plane). The electron correlation correction to the above values is estimated from coupled cluster calculations as Θxx=−0.12 and \documentclass{article}\pagestyle{empty}\begin{document}$\Theta_{zz}=-0.34\ ea_{0}^{2}$\end{document} for the quadrupole and Φxxxx=1.26, Φyyyy=−1.30, and \documentclass{article}\pagestyle{empty}\begin{document}$\Phi_{zzzz}=1.80\ ea_{0}^{4}$\end{document} for the hexadecapole moment. For the halogenated ethenes we have obtained the following quadrupole moment values from second‐order Mø ller–Plesset perturbation theory calculations: Θxx=−1.14 (C2F4), 1.94 (C2Cl4), 3.61 (C2Br4), 6.84 (C2I4) and Θzz=−1.04 (C2F4), −0.41 (C2Cl4), −0.15 (C2Br4), −0.87 (C2I4) \documentclass{article}\pagestyle{empty}\begin{document}$ea_{0}^{2}$\end{document}. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Calculations of the atomic and electronic structure for SrTiO 3 perovskite thin films

The results of calculations of SrTiO 3 (100) surface relaxation and rumpling with two different terminations (SrO and TiO 2) are presented and discussed. We have used the ab initio Hartree–Fock (HF) method with electron correlation corrections and the density functional theory (DFT) with different exchange–correlation functionals, including hybrid exchange techniques. All methods agree well on surface energies and on atomic displacements, as well as on the considerable increase of covalency effects near the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing of theoretical predictions.

Ab initiomodeling of surface structure forSrTiO3perovskite crystals

We present and discuss the results of calculations of ${\mathrm{SrTiO}}_{3}$ (100) surface relaxation and rumpling with two different terminations (SrO and ${\mathrm{TiO}}_{2}).$ These are based on ab initio Hartree-Fock method with electron correlation corrections and density functional theory calculations with different exchange-correlation functionals, including hybrid exchange techniques. Both approaches use the localized Gaussian-type basis set. All methods agree well on surface energies and on atomic displacements, as well as on considerable increase of covalency effects nearby the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing theoretical predictions.

A quantum‐chemical study of PBX: intermolecular interactions of TATB with CH2F2 and with linear fluorine‐containing polymers

AbstractThe calculations of density functional theory at the B3LYP/3‐21G* level have been employed to optimize the 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB)CH2F2 complex. The complex binding energy is corrected for the basis set superposition error. In addition, the interactions of TATB with (CUVCXY) n (U, V, X, Y = H. U = F; V, X, Y = H. U, V = F; X, Y = H. U, V, X = F; Y = H. U, V, X, Y = F. U, V, X = F; Y = Cl) have been studied with the MO‐PM3 method, and the complex binding energy with approximation of electron correlation correction by the dispersion energy has been given. The results computed indicate that the greatest corrected binding energy of TATB and CH2F2 is −4.62 kJ mol−1 at the B3LYP/6‐311G*//B3LYP/3‐21G* level. The interactions of ­(CF2CH2) n with TATB and of (CF2CFH) n with TATB are stronger than those of (CUVCXY) n (U, V, X, Y = H. U = F; V, X, Y = H. U, V, X, Y = F. U, V, X = F; Y = Cl) with TATB (n = 5). Copyright © 2001 John Wiley & Sons, Ltd.

Cluster simulations of structural transformations in yellow arsenic

Yellow arsenic (y-As) consists of tetrahedral As 4 molecules that may be packed in some amorphous and crystalline structures. Like many other arsenic structures, y-As is metastable and undergoes irreversible transitions (polymerization) under irradiation. The process of y-As polymerization, which is observed experimentally, usually leads to the formation of amorphous arsenic (a-As) possessing a continuous random network structure. Our previous quantum chemical simulation for an eight-atom cluster model performed using semi-empirical CNDO/BW approach, combined with optimization technique of cyclic coordinate descent, have shown a formation of molecular dimers due to breaking of one bond in each tetrahedral As 4 molecule accompanied with bond switching over to chair-like structure. In that case a pair of approaching As 4 molecules is positioned in a staggered “face-to-face” configuration ( D 2 d symmetry), which may be considered as a conformation with a six-membered chair-shaped ring dominating in the structure of a polymerized a-As. Two energetically preferable configurations of an As 8 cluster have been found here after careful semi-empirical optimization of the face-to-face structure: they possess either cubane configuration ( O h symmetry) or eclipsed “edge-to-edge” configuration ( D 2 h symmetry). For the first time, a two-dimensional energy surface E( z, θ) has been calculated in order to analyze possible paths of structural transformations in y-As. Analogous qualitative results have been just obtained by us when using ab initio Hartree–Fock method combined with the electron correlation corrections for eight-atom cluster model of molecular arsenic. A comparison of both quantum chemical simulations, together with data from previous experimental studies allows us to describe a possible mechanism of the initial stage of the polymerization of y-As.

An ab initio study of the structures and energetics of the planar ground and 90°‐twisted excited states of substituted ethylenes

AbstractAb initio molecular orbital calculations are performed on the planar ground states (S0), the 90°‐twisted triplet (T1), and pyramidalized singlet (S1) excited states of ethylene, methaniminium cation (MC), monocyano‐ (MCE), 1,1‐dicyano‐ (DCE), 1,1‐dihydroxy‐ (DHE), and 1,1‐dicyano‐2,2‐dihydroxy (DCHE) ethylenes. Equilibrium geometries are optimized at the Hartree–Fock (HF) level with the 6‐31G* basis set. Electron correlation corrections are estimated by optimizing the HF/6‐31G* geometries at the (U)MP2/6‐31G* level and then by carrying out single‐point calculations at the fourth‐order Møller–Plesset perturbation theory ((U)MP4/6‐311G**//MP2/6‐31G*). The effects of various types of perturbations on the structures, energetics, dipole moments, and state ordering of S0, S1, and T1 are carefully investigated. “Positive” S1–T1 splittings are estimated at the HF level for all studied molecules, while “negative” S1–T1 splittings are obtained at the MP2 level for MC, DHE, and DCHE. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 242–254, 2001

Calculations of Surface Structure for SrTiO3 Perovskite

ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. OurSM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments.

Origin of the Attraction and Directionality of the NH/π Interaction: Comparison with OH/π and CH/π Interactions

High-level ab initio calculations were carried out to evaluate the interaction between the π face of benzene and ammonia as a model of NH/π interaction. The intermolecular interaction energy was calculated from the extrapolated MP2 interaction energy at the basis set limit and a CCSD(T) correction term. The calculated interaction energy (−2.22 kcal/mol) is considerably smaller than that of the hydrogen bond between waters. The monodentate complex is slightly more stable than the bidentate and tridentate complexes. The potential energy surface is very flat near the minimum, which shows that the major source of the attraction is a long-range interaction. The HF interaction energy of the monodentate complex (0.13 kcal/mol) is repulsive. The large gain in the attraction by electron correlation correction (−2.36 kcal/mol) indicates that the dispersion interaction is significantly important for the attraction. The electrostatic energy (−1.01 kcal/mol) is also important for the attraction. The benzene−water (OH/...

Parallel aspects of quantum molecular dynamics simulations of liquids

A very straightforward parallel scheme to perform Born–Oppenheimer quantum molecular dynamics simulations of liquids is presented. It is analogous to Linear Scaling methods, used in electronic structure calculations. The instantaneous liquid configurations of molecules moving in the simulation cell with periodic boundaries and minimum image convention are divided into smaller spherical clusters around each molecule. Forces, acting on the nuclei of the molecule in the middle of each cluster, are calculated independently at any suitable level of quantum mechanical sophistication. From low-end semi-empirical schemes to high-end methods containing electron correlation corrections. In this communication selected results from simulations of liquid water simulated at 300K and normal density using ab initio Hartree–Fock level with three different basis sets are presented. Good results are obtained for the near-structure and other characteristic liquid properties of water. A simple way to implement the method by combining a conventional classical MD simulation code with any quantum chemistry package capable of performing force calculations is presented. Suggestions of suitable parallel schemes based on standard message passing techniques are given. Performance, scaling and load balancing properties are discussed and possible future directions are suggested.

Many-body Green’s-function calculations on the electronic excited states of extended systems

Electron correlation corrections to the excitation energy of the lowest-lying singlet exciton state of polyethylene are evaluated with the aid of the quasiparticle energies obtained from second-order many-body perturbation theory and from the second-order inverse Dyson equation. A simple approximation is proposed to avoid the evaluation of the quasiparticle energies for high- and low-lying energy bands, which is particularly problematic in extended-system calculations. The inclusion of both the electron correlation effects and diffuse basis functions is important for the proper description of the exciton state. The electron correlation corrections calculated by this method appear to be too large, probably due to the neglect of the screening effects of the quasiparticle interactions.

The Magnitude of the CH/π Interaction between Benzene and Some Model Hydrocarbons

High-level ab initio calculations were carried out to evaluate the interaction between the π face of benzene and hydrocarbon molecules (methane, ethane, ethylene, and acetylene). Intermolecular interaction energies were calculated from extrapolated MP2 interaction energies at the basis set limit and CCSD(T) correction terms. The calculated benzene−methane interaction energy (−1.45 kcal/mol) is considerably smaller than that of the hydrogen bond between waters. The benzene−methane complex prefers a geometry in which the C−H bond points toward the benzene ring. The potential energy surface is very flat near the minimum, which shows that the major source of the attraction is a long-range interaction. The HF interaction energy of the complex (0.85 kcal/mol) is repulsive. The large gain of the attraction energy (−2.30 kcal/mol) by electron correlation correction indicates that dispersion interaction is the major source of the attraction. Although the electrostatic energy (−0.25 kcal/mol) is small, a highly ori...

Anab initio interpretation in gas phase and aqueous solution of the generalized anomeric effect in R?O?CR2?NR2 (R = H, CH3)

The conformational stability of aminomethanol and its methylated derivatives has been investigated by means of ab initio methods in the gas phase and aqueous solution. Among the computational levels employed, HF/6-31G**//HF/6-31G** calculations correctly describe the conformational features of this series of compounds, and agree well with the results obtained using larger basis sets and including ZPE or electron correlation corrections. Calculated energies and geometries follow the known trends associated to the generalized anomeric effect. Thus, the most stable conformers exhibit preferences for the trans orientations of the LpN CO and LpOCN moieties. However, reverse anomeric effects are observed when a methyl group is bonded to the oxygen, because the LpOCN unit prefers a gauche orientation (that is, trans MeOCN). The natural bond orbital (NBO) method was employed to explain the cited conformational preferences. According to the NBO results, trans arrangements are preferred because the stabilization due to charge delocalization is more important than electrostatic and steric contributions. This explanation agrees with the conclusions obtained by other independent procedures based on energy decomposition schemes. The NBO method was also used to explain the origin of the rotational barriers around the C O and CN bonds in terms of the balance between unfavorable hyperconjugation and electrostatic and steric effects. Changes in conformational stability caused by methylations in different molecular positions were also explained by the influence of the methyl groups on lone-pair delocalization and on steric effects. Finally, the effect of solvation was studied by means of the ab initio PCM method, and the significant changes on relative energies found were analyzed. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 462–477, 2000

Effects of the higher electron correlation correction on the calculated intermolecular interaction energies of benzene and naphthalene dimers: comparison between MP2 and CCSD(T) calculations

Intermolecular interaction energies of parallel and T-shape benzene dimers and parallel naphthalene dimer were calculated with MP2, MP3, MP4(SDQ), MP4(SDTQ), CCSD and CCSD(T) electron correlation corrections using several basis sets. The MP2 calculations considerably overestimated the attraction compared to the CCSD(T) ones. The MP2 correlation interaction energies, the differences between the HF and MP2 interaction energies, were 21–38% larger than the corresponding CCSD(T) ones. The MP4(SDQ) and CCSD calculations substantially underestimated the attraction compared to MP4(SDTQ) and CCSD(T), which indicated the importance of triple excitation. The estimated CCSD(T) interaction energies of the three dimers with reasonably large basis sets were −1.74, −2.50 and −5.69 kcal/mol, respectively.

Basis set and electron correlation effects on the first and second static hyperpolarizability of SO 2

Accurate values are reported for the static hyperpolarizability of SO 2. We have obtained near-Hartree–Fock SCF values of μ z =−0.7916 e a 0 for the dipole moment, α ̄ =23.59 and Δ α=11.73 e 2 a 0 2 E h −1 for the mean and the anisotropy of the dipole polarizability, β ̄ =35.0 e 3 a 0 3 E h −2 for the mean first and γ ̄ =2061 e 4 a 0 4 E h −3 for the mean second dipole hyperpolarizability. Our CCSD(T) values for the electron correlation correction to these properties are −0.1676 e a 0, 2.25 and 1.38 e 2 a 0 2 E h −1, −4.8 e 3 a 0 3 E h −2 and 1325 e 4 a 0 4 E h −3. The mean β ̄ =30.1 e 3 a 0 3 E h −2 and γ ̄ =3390 e 4 a 0 4 E h −3 are larger than the experimental Kerr effect values at 632.8 nm.

High-Level ab Initio Calculations of Torsional Potential of Phenol, Anisole, and o-Hydroxyanisole: Effects of Intramolecular Hydrogen Bond

The internal rotational barrier heights of phenol and anisole were calculated using several basis sets up to cc-pVQZ with MP2-level electron correlation correction to evaluate the basis set effects. The calculations showed that the effects of the further improvement of the basis set beyond the cc-pVTZ were very small. Although the electron correlation substantially increased the barrier heights of the two molecules, the effects of the electron correlation beyond the MP2 method were not large. The barrier heights calculated with the CCSD(T) method were close to those with the MP2 method. The internal rotational potentials of methoxy and hydroxyl groups of o-hydroxyanisole were calculated at the MP2/cc-pVTZ//HF/6-311G** level. The calculated potentials were compared with those of phenol and anisole. o-Hydroxyanisole preferred planar structure in which the hydroxyl group had an intramolecular hydrogen bond with the oxygen atom of the methoxy group. The calculated torsional potential of the methoxy group had the maximum (7.30 kcal/mol) when the methoxy group rotated 180° from the minimum energy structure, in which the hydroxyl group did not have the hydrogen bond. The barrier height of the methoxy group of o-hydroxyanisole was considerably larger than that of anisole (2.99 kcal/mol). The large internal rotational barrier height of o-hydroxyanisole showed that the intramolecular hydrogen bond greatly stabilized the energy minimum structure and that the hydrogen bond strictly restricted the conformational flexibility of the methoxy group.