The Experts below are selected from a list of 2289 Experts worldwide ranked by ideXlab platform
Örs Legeza - One of the best experts on this subject based on the ideXlab platform.
-
On the calculation of complete dissociation curves of closed-shell pseudo-onedimensional systems through the Multireference Method of increments
The Journal of chemical physics, 2015Co-Authors: Edoardo Fertitta, Beate Paulus, Gergely Barcza, Örs LegezaAbstract:The Method of Increments (MoI) has been employed using a Multireference approach to calculate the dissociation curve of beryllium ring-shaped clusters Be$_n$ of different sizes. Benchmarks obtained through different single and Multireference Methods including the ab initio Density Matrix Renormalization Group (DMRG) were used to verify the validity of the MoI truncation which showed a reliable behavior for the whole dissociation curve. Moreover we investigated the size dependence of the correlation energy at different distances in order to extrapolate the values for the periodic chain and to discuss the transition from a metal-like to a insulating-like behavior of the wave function through quantum chemical considerations.
-
Tree Tensor Network State with Variable Tensor Order: An Efficient Multireference Method for Strongly Correlated Systems
Journal of chemical theory and computation, 2015Co-Authors: Valentin Murg, Frank Verstraete, Reinhold Schneider, Péter R. Nagy, Örs LegezaAbstract:We study the tree-tensor-network-state (TTNS) Method with variable tensor orders for quantum chemistry. TTNS is a variational Method to efficiently approximate complete active space (CAS) configuration interaction (CI) wave functions in a tensor product form. TTNS can be considered as a higher order generalization of the matrix product state (MPS) Method. The MPS wave function is formulated as products of matrices in a multiparticle basis spanning a truncated Hilbert space of the original CAS-CI problem. These matrices belong to active orbitals organized in a one-dimensional array, while tensors in TTNS are defined upon a tree-like arrangement of the same orbitals. The tree-structure is advantageous since the distance between two arbitrary orbitals in the tree scales only logarithmically with the number of orbitals N, whereas the scaling is linear in the MPS array. It is found to be beneficial from the computational costs point of view to keep strongly correlated orbitals in close vicinity in both arrange...
Mark S. Gordon - One of the best experts on this subject based on the ideXlab platform.
-
Multireference second-order perturbation theory: how size consistent is "almost size consistent".
The Journal of chemical physics, 2005Co-Authors: Jamie Marie Rintelman, Ivana Adamovic, Sergey A. Varganov, Mark S. GordonAbstract:A systematic study of the deviation from size consistency of the Multireference second-order Moller-Plesset perturbation theory (MRMP2) Method is presented. The size-consistency error is shown to depend on the number of monomers in a supermolecule calculation, size of basis set, number of correlated valence electrons, and size of active space. HF, F2, and N2 are used as test cases, with stretched bonds, to include simple, well-defined Multireference character. This is essential in ensuring that MRMP2 is being tested as a Multireference Method. It is concluded that the MRMP2 and other Multireference perturbation theory Methods can exhibit significant size-consistency errors, and that the size of the error depends on the manner in which the perturbation theory is implemented.
Troy Van Voorhis - One of the best experts on this subject based on the ideXlab platform.
-
Configuration interaction based on constrained density functional theory: a Multireference Method.
The Journal of chemical physics, 2007Co-Authors: Chiao-lun Cheng, Troy Van VoorhisAbstract:Existing density functional theory (DFT) Methods are typically very effective in capturing dynamic correlation, but run into difficulty treating near-degenerate systems where static correlation becomes important. In this work, we propose a configuration interaction (CI) Method that allows one to use a Multireference approach to treat static correlation but incorporates DFT’s efficacy for the dynamic part as well. The new technique uses localized charge or spin states built by a constrained DFT approach to construct an active space in which the effective Hamiltonian matrix is built. These local configurations have significantly less static correlation compared to their delocalized counterparts and possess an essentially constant amount of self-interaction error. Thus their energies can be reliably calculated by DFT with existing functionals. Using a small number of local configurations as different references in the active space, a simple CI step is then able to recover the static correlation missing from ...
-
configuration interaction based on constrained density functional theory a Multireference Method
Journal of Chemical Physics, 2007Co-Authors: Chiao-lun Cheng, Troy Van VoorhisAbstract:Existing density functional theory (DFT) Methods are typically very effective in capturing dynamic correlation, but run into difficulty treating near-degenerate systems where static correlation becomes important. In this work, we propose a configuration interaction (CI) Method that allows one to use a Multireference approach to treat static correlation but incorporates DFT's efficacy for the dynamic part as well. The new technique uses localized charge or spin states built by a constrained DFT approach to construct an active space in which the effective Hamiltonian matrix is built. These local configurations have significantly less static correlation compared to their delocalized counterparts and possess an essentially constant amount of self-interaction error. Thus their energies can be reliably calculated by DFT with existing functionals. Using a small number of local configurations as different references in the active space, a simple CI step is then able to recover the static correlation missing from the localized states. Practical issues of choosing configurations and adjusting constraint values are discussed, employing as examples the ground state dissociation curves of H(2) (+), H(2), and LiF. Excellent results are obtained for these curves at all interatomic distances, which is a strong indication that this Method can be used to accurately describe bond breaking and forming processes.
Aristides Mavridis - One of the best experts on this subject based on the ideXlab platform.
-
Ab initio investigation of the ground state properties of PO, PO+, and PO−
The Journal of Chemical Physics, 2003Co-Authors: Aristophanes Metropoulos, Aristotle Papakondylis, Aristides MavridisAbstract:We have computed accurate potential energy curves of the ground states of the PO(X 2Π), PO+(X 1Σ+) and PO−(X 3Σ−) species by Multireference configuration interaction and coupled-cluster Methods and have obtained accurate spectroscopic constants for each species. We have also determined the effect of core on the properties above and have obtained the PO complete basis set limit by the Multireference Method for the equilibrium energy, bond distance, dissociation energy, harmonic frequency, and dipole moment.
Kyungwha Park - One of the best experts on this subject based on the ideXlab platform.
-
Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets.
The journal of physical chemistry. A, 2019Co-Authors: Ryan Pederson, Aleksander L. Wysocki, Nicholas J. Mayhall, Kyungwha ParkAbstract:We investigate how different chemical environments influence magnetic properties of terbium(III) (Tb)-based single-molecule magnets (SMMs), using first-principles relativistic Multireference Method...
