On the performance of molecular model core potential orbitals in spin-orbit and electron correlation studies

1996 ◽  
Vol 74 (6) ◽  
pp. 1248-1252 ◽  
Author(s):  
Dietmar Krause ◽  
Mariusz Klobukowski
Keyword(s):  
Electron Correlation ◽  
Correlation Energy ◽  
Molecular Model ◽  
Virtual Space ◽  
Coupling Constants ◽  
Basis Sets ◽  
Spin Orbit ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Model Core Potentials

The role of improved parametrization and accurate basis sets in model core potentials was studied in calculations of the spin-orbit coupling constants (in PH, AsH, and SbH) and of the electron correlation effects (in P2, As2, and Sb2). An effective method of identifying and removing the intruder quasi-core orbitals from the virtual orbital space was proposed in connection with the post-Hartree–Fock calculations. The results demonstrated that (a) the flexible valence basis sets allow evaluation of the spin-orbit effects without resorting to any scaling techniques and (b) the intruder quasi-core orbitals, even if left imbedded in the virtual space, have negligible effect on the values of the electron correlation energy. Key words: effective core potentials, basis sets, spin-orbit effects, electron correlation.

An approximate ab initio method based on the DIM model

2000 ◽  
Vol 78 (12) ◽  
pp. 1575-1586 ◽  
Author(s):  
John M Cullen
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Basis Sets ◽  
Ab Initio Method ◽  
First Order ◽  
Hartree Fock ◽  
Modified Method ◽  
Electron Correlation Energy

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.

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.

Spin–Orbit Coupling Constants in Atoms and Ions of Transition Elements: Comparison of Effective Core Potentials, Model Core Potentials, and All-Electron Methods

2019 ◽  
Vol 123 (12) ◽  
pp. 2325-2339 ◽  
Author(s):  
Shiro Koseki ◽  
Nikita Matsunaga ◽  
Toshio Asada ◽  
Michael W. Schmidt ◽  
Mark S. Gordon
Keyword(s):  
Coupling Constants ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Transition Elements ◽  
Model Core Potentials ◽  
Effective Core Potentials

Calculation of Second- and Higher-Order Force Constants Including Electron Correlation Effects and Hartree-Fock Force Constant Scaling

2003 ◽  
Vol 44 (4) ◽  
pp. 538-545
Author(s):  
B. K. Novosadov ◽  
Yu. I. Tarasov ◽  
D. M. Kovtun ◽  
I. V. Kochikov
Keyword(s):  
Force Constant ◽  
Electron Correlation ◽  
Higher Order ◽  
Force Constants ◽  
Correlation Effects ◽  
Hartree Fock ◽  
Electron Correlation Effects

scholarly journals Hyperfine Coupling Constants in Local Exact Two-Component Theory

2021 ◽  
Author(s):  
Yannick J. Franzke ◽  
Jason M. Yu
Keyword(s):  
Single Molecule ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Scalar Potential ◽  
Coupling Constants ◽  
Basis Set ◽  
Basis Sets ◽  
Spin Orbit ◽  
Finite Nucleus ◽  
Two Component

We present a highly efficient implementation of the electron-nucleus hyperfine coupling matrix within one-electron exact two-component (X2C) theory. The complete derivative of the X2C Hamiltonian is formed, i.e. the derivatives of the unitary decoupling transformation are considered. This requires solution of the response and Sylvester equations, consequently increasing the computational costs. Therefore, we apply the diagonal local approximation to the unitary decoupling transformation (DLU). The finite nucleus model is employed for both the scalar potential and the vector potential. Two-electron picture-change effects are modeled with the (modified) screened-nuclear spin--orbit approach. Our implementation is fully integral direct and OpenMP-parallelized. An extensive benchmark study regarding the Hamiltonian, the basis set, and the density functional approximation is carried out for a set of 12--17 transition-metal compounds. The error introduced by DLU is negligible and the DLU-X2C Hamiltonian accurately reproduces its four-component ``fully'' relativistic parent results. Functionals with a large amount of Hartree--Fock exchange such as CAM-QTP-02 and omega-B97X-D are generally favorable. The pure density functional r2SCAN performs remarkably and even outperforms the common hybrid functionals TPSSh and CAM-B3LYP. Fully uncontracted basis sets or contracted quadruple-zeta bases are required for accurate results. The capability of our implementation is demonstrated for [Pt(C6Cl5)4]- with more than 4700 primitive basis functions and four rare-earth single molecule magnets: [La(OAr*)3]-, [Lu(NR2)3]-, [Lu(OAr*)3]-, and [TbPc2]-. Here, the spin--orbit DLU-X2C Hamiltonian results in an excellent agreement with the experimental findings of all Pt, La, Lu, and Tb molecules.

Simplified Non-Empirical Unrestricted Hartree-Fock Approximation (SUHF) for the Calculation of Electronic Ground State Properties of Molecules with Closed and Open Valence Shells. I. Method

1993 ◽  
Vol 48 (7) ◽  
pp. 829-833
Author(s):  
Wolfhard Koch
Keyword(s):  
Electron Correlation ◽  
Ground State ◽  
Atomic Orbital ◽  
Closed Shell ◽  
Open Shell ◽  
Polyatomic Molecules ◽  
Correlation Effects ◽  
Hartree Fock ◽  
Electron Correlation Effects ◽  
Electronic Ground

Abstract Focusing on relative stabilities of electronic states with different spin multiplicities of polyatomic molecules, a simplified unrestricted Hartree-Fock (SUHF) procedure is described. Using different orbitals for different spins (DODS), electron correlation effects of both closed-shell and open-shell systems are expected to be taken into account in the simplest way. While working within a symmetrically orthogonalized (Löwdin) basis we make use of the NDDO approximation (neglect of diatomic differential overlap) concerning the evaluation of electron repulsion and nuclear attraction integrals. Originally, a locally orthogonalized all-electron atomic orbital set of Slater type is considered. The approximation method is completely non-empirical. Rotational invariance is fully retained.

Sign in / Sign up

Export Citation Format

Share Document