scholarly journals Electron Correlation Effects on the Longitudinal Polarizabilities and Second Hyperpolarizabilities of Polyenes: A Finite Field Study

2014 ◽  
Vol 2014 ◽  
pp. 1-6
Author(s):  
Qingxu Li ◽  
Xianju Zhou ◽  
Shiwei Yin
Keyword(s):  
Finite Field ◽  
Electron Correlation ◽  
Density Functional ◽  
Basis Sets ◽  
Functional Theory ◽  
Conjugated Polyenes ◽  
Quantitative Results ◽  
Electron Correlation Effects ◽  
Longitudinal Polarizability ◽  
Moller Plesset

We carry out ab initio calculations, based on finite-field scheme, of the longitudinal polarizabilities (αL) and second hyperpolarizabilities (γL) of conjugated polyenes, and study the effects of electron correlation, with second-order Moller-Plesset perturbation theory and coupled cluster with singles and doubles method. Calculations with density functional theory are also made to compare with wave-function based methods. Our study shows that electron correlation reduces linear longitudinal polarizability and enhances longitudinal second hyperpolarizability for short polyenes, but the effects decrease as the chain increases; choosing appropriate basis sets is important when quantitative results are required.

Electron correlation effects in small iron clusters

2004 ◽  
Vol 1 (4) ◽  
pp. 288-296 ◽  
Author(s):  
G. Rollmann ◽  
P. Entel
Keyword(s):  
Electron Correlation ◽  
Density Functional ◽  
Magnetic Moments ◽  
Coulomb Repulsion ◽  
Correlation Effects ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Jahn Teller ◽  
Electron Correlation Effects ◽  
Ground State Structures

We present results of first-principles calculations of structural, magnetic, and electronic properties of small Fe clusters. It is shown that, while the lowest-energy isomers of Fe3 and Fe4 obtained in the framework of density functional theory within the generalized gradient approximation (GGA) are characterized by Jahn-Teller-like distortions away from the most regular shapes (which is in agreement with other works), these distortions are reduced when electron correlation effects are considered explicitly as within the GGA+U approach. At the same time, the magnetic moments of the clusters are enhanced with respect to the pure GGA case, resulting in maximal moments (in the sense of Hund’s rules) of 4 μB per atom for the ground state structures of Fe3 and Fe4, and a total moment of 18 μB for Fe5. This already happens for moderate values of the Coulomb repulsion parameter U̴ 2.0 eV and is explained by changes in the electronic structures of the clusters.

QUANTUM CHEMICAL STUDY OF CISPLATIN-WATER COMPLEXES: AN INVESTIGATION OF ELECTRON CORRELATION EFFECTS

2011 ◽  
Vol 10 (03) ◽  
pp. 371-391 ◽  
Author(s):  
JULIANA FEDOCE LOPES ◽  
JÚLIO C. S. DA SILVA ◽  
WILLIAN R. ROCHA ◽  
WAGNER B. DE ALMEIDA ◽  
HÉLIO F. DOS SANTOS
Keyword(s):  
Interaction Energy ◽  
Electron Correlation ◽  
Density Functional ◽  
Correlation Energy ◽  
Strong Dependence ◽  
Quantum Chemical Study ◽  
Basis Sets ◽  
Correlation Effects ◽  
Multipole Expansion Method ◽  
Electron Correlation Effects

The interaction of cisplatin ([ Pt(NH3)2Cl2] ) with water was studied for distinct complexation modes aiming to investigate the level of calculation required to describe transition metal complexes of biological relevance, where large scale ab initio post-Hartree-Fock calculations are usually precluded. Coupled Cluster (CCSD(T)) single point calculations employing MP2 and MP4(SDQ) optimized geometries and good quality basis sets, using effective core potential for platinum atom, are reported as well as Density Functional Theory (DFT) results employing various exchange-correlation functional. The importance of electron correlation effects for the calculation of interaction energies is discussed. The extension of correlation energy recovered by DFT was assessed considering the CCSD(T) results as reference. The recently developed M06-2x functional showed the best overall agreement with CCSD(T) calculations. The relative importance of the electrostatic and dispersion contributions to the interaction energy was estimated with the aid of the atoms in molecules theory and also using an empirical approach based on the multipole expansion method. It was found a strong dependence of the energy contributions on the spatial orientation of water and cisplatin monomers, with the electrostatic contribution dominating the interaction energy for the lowest energy equilibrium structures.

Quantum chemistry computations of properties of acrylamide dimers

2014 ◽  
Vol 1709 ◽  
Author(s):  
Yi-Siang Wang ◽  
Yi-De Lin ◽  
Sheng D. Chao
Keyword(s):  
Density Functional Theory ◽  
Perturbation Theory ◽  
Density Functional ◽  
Basis Sets ◽  
Medium Size ◽  
Functional Theory ◽  
Equilibrium Configurations ◽  
Correlation Consistent ◽  
Consistent Basis ◽  
Moller Plesset

ABSTRACTIntermolecular interaction potentials of the acrylamide dimer in 12 equilibrium configurations have been calculated using the second-order Møller-Plesset (MP2) perturbation theory. We have employed Pople’s medium size basis sets [up to 6-311++G(3df,2p)] and Dunning’s correlation consistent basis sets (up to aug-cc-pVTZ). We have also carried out density functional theory (DFT) type calculations and compared the results with those calculated with the MP2 theory.

Bonding analysis for sterically uncongested simple aurocarbons CnAum

2009 ◽  
Vol 87 (7) ◽  
pp. 798-801 ◽  
Author(s):  
Patryk Zaleski-Ejgierd ◽  
Pekka Pyykkö
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Formation Energy ◽  
Basis Sets ◽  
Bonding Mechanism ◽  
Functional Theory ◽  
Bonding Analysis ◽  
Thermodynamical Properties ◽  
Moller Plesset ◽  
Plesset Perturbation Theory

The title series of simple model aurocarbons, CAu4, C2Au2, C2Au4, C2Au6, and C6Au6, is investigated using density functional theory with TPSS and B3LYP functionals and the second-order Møller–Plesset perturbation theory, with the latest Karlsruhe basis sets. The vibrational frequencies and the 0 K thermodynamical properties are calculated. The bonding mechanism is also investigated. For C2Aun the calculated MP2 formation energy suggests increased stabilization with increasing n, due to the Au–Au aurophilic pair interactions.

STUDY OF INTRAMOLECULAR HYDROGEN BONDING IN ORTHO-SUBSTITUTED ACETANILIDE COMPOUNDS USING COMPUTATIONAL METHODS

2004 ◽  
Vol 03 (04) ◽  
pp. 527-542 ◽  
Author(s):  
SEIFOLLAH JALILI ◽  
MOJDEH AKHAVAN
Keyword(s):  
Hydrogen Bonding ◽  
Density Functional ◽  
Structural Parameters ◽  
Intramolecular Hydrogen Bonding ◽  
Basis Sets ◽  
Structural Factors ◽  
Functional Theory ◽  
Aim Theory ◽  
Moller Plesset ◽  
Intramolecular Hydrogen

The intramolecular hydrogen bonding formation in ortho-substituted compounds of Acetanilide, ortho-hydroxy Acetanilide and ortho-nitro Acetanilide, was investigated using Density Functional Theory (DFT), Møller-Plesset second-order (MP2) method and "Atoms in Molecules (AIM)" theory. It was found that in each case, the cis isomer is more stable than the trans isomer and ortho-nitro Acetanilide forms a stronger hydrogen bond than ortho-hydroxy Acetanilide. The effects of hydrogen bonding on structural parameters of the considered systems were studied using Becke's functional (B3LYP) and at the ab initio MP2 level in conjunction with different basis sets and suitable structural factors. The results are in agreement with the results of AIM theory.

Basis set effects in simple compounds of heavy rare gases

2013 ◽  
Vol 91 (9) ◽  
pp. 894-901 ◽  
Author(s):  
Amelia Fitzsimmons ◽  
Mariusz Klobukowski
Keyword(s):  
Density Functional ◽  
Relativistic Effects ◽  
Basis Set ◽  
Basis Sets ◽  
Rare Gas ◽  
Rare Gases ◽  
Functional Theory ◽  
Model Core Potentials ◽  
Moller Plesset ◽  
Decomposition Pathway

Rare-gas hydrides of the type HRgX (Rg = Xe or Rn and X = F, Cl, Br, or I) have been studied using Møller–Plesset and density functional theory methods. Six model core potentials and their associated basis sets were used, with relativistic effects included implicitly. The effects of polarization, correlating, and diffuse basis functions were investigated. Molecular geometries of the metastable hydrides and transition states along the decomposition pathway were computed together with corresponding energies of formation and decomposition. The results of quantum theory of atoms in molecules analysis further elucidate the interactions between atoms in HRgX species and confirm the results of analyses obtained from the natural bond orbitals approach.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

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