162,227 research outputs found
Explicitly correlated multireference coupled cluster computations
No full textTitle: Explicitly Correlated Multireference Coupled Cluster Computations Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies for the bent singlet state of carbene molecule were calculated using post-HF CCSD, CCSD-F12, MR BWCSSD, and MR BWCC- SD-F12 methods. Main aim of the thesis was to compare the energy con- vergence with respect to cardinal number X of the basis set used for the conventional MR BWCCSD method and its explicitly correlated counter- part. Also, weights of the references within the multireference calculations were compared. It was shown that use of explicit correlation within the mul- tireference approach, as well as for the single-reference approach, speeds up the convergence of energy by an order when considering the cardinal number of basis set. Keywords: coupled clusters, multireference, explicitly correlated, F12, car- bene
Studium diradikálů multireferenčními metodami spřažených klastrů s explicitní korelací
No full textNázev práce: Studium diradikálů multireferenčními metodami spřažených klastrů Autor: Matej Švaňa Katedra: Katedra fyzikální a makromolekulární chemie Vedoucí diplomové práce: Mgr. Jiří Pittner, Dr. rer. nat., Ústav fyzikální chemie J. Heyrovského Abstrakt: Tematem diplomové práce je studium isomerizace cyklopropánu přes trimetylénový/propylidénový diradikál pomocí jednak konvenční a jed- nak multireferenční metody vázaných klastrů. Hlavním cílem bylo srovnat konvergenci získaných energií s velikostí použité báze pro konvenční a explic- itně korelované MRCC výpočty. Podle očekávání výsledky ukázaly, že explic- itní korelace vede k výraznému zlepšení konvergence (cca o jedno kardinální číslo), což umožňuje výrazné úspory výpočetního času. Navíc výpočty po- mocí MkCCSD(T)-F12/QZ a BWCCSD(T)-F12/QZ metod patří mezi ty ne- jsofistikovanejší, jaké kdy byli na výpočet relativní energií cyklopropánu a trimetylénu/propylidénu použity. Klíčová slova: explicitně korelované, spřažené klastry, multireferenční, isomerizace cyclopropánu, trimetylén, propylidén 1Title: Study of Diradicals by Explicitly Correlated Multireference Coupled Cluster Methods Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies of cyclopropane, trimethylene, and propylidene were calculated with conventional post-HF CCSD(T), BWCCSD(T), MkCCSD(T) methods and their explicitly correlated alternatives. Main aims of the the- sis were to compare the basis set convergence of total energies and relative energies between cyclopropane and trimethylene/propylidene, both at the conventional and the explicitly correlated levels. It was shown that use of explicit correlation accelerates the convergence of the total energy by one or- der of basis set quality, resulting in considerable savings in computational times. Also, the MkCCSD(T)-F12/QZ and the BWCCSD(T)-F12/QZ calcula- tions belong to the most sophisticated approaches employed for estimation of the relative energies of cyclopropane and trimethylene/propylidene to date. Keywords: explicitly correlated, coupled cluster, multi-reference, cyclopropane isomerisation, trimethylene, propylidene 1Katedra fyzikální a makromol. chemieDepartment of Physical and Macromolecular ChemistryPřírodovědecká fakultaFaculty of Scienc
Výpočty pomocí explicitně korelované multireferenční metody spřažených klastrů
No full textNázev práce: Výpočty pomocí explicitně korelované multireferenční metody spřažených klastrů Autor: Matej Švaňa Katedra: Katedra fyzikální a makromolekulární chemie Vedoucí bakalářské práce: Mgr. Jiří Pittner, Dr. rer. nat., Ústav fyzikální chemie J. Heyrovského AV ČR Abstrakt: Celkový energie singletového stavu karbenu byly napočítaný po- mocí post-HF metod CCSD, CCSD-F12, MR BWCCSD, a MR BWCCSD- F12. Hlavním cílem práce bylo porovnat závislost konvergence celkový en- ergie na kardinálním číslu použitých bází pro konvenční metodu MR BWCCSD a explicitně korelovanou metodu MR BWCCSD-F12. Byly prostudovaný váhy jednotlivých referencí týkající se výpočtů multireferenčních metod. Výs- ledky ukázali, že použití explicitní korelace v multireferenčních metodách, stejně jako v jednoreferenčních metodách, urychluje konvergenci energie o jedno kardinální číslo báze. Klíčová slova: spřažené klastry, multireferenční, explicitně korelované, F12, karben 1Title: Explicitly Correlated Multireference Coupled Cluster Computations Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies for the bent singlet state of carbene molecule were calculated using post-HF CCSD, CCSD-F12, MR BWCSSD, and MR BWCC- SD-F12 methods. Main aim of the thesis was to compare the energy con- vergence with respect to cardinal number X of the basis set used for the conventional MR BWCCSD method and its explicitly correlated counter- part. Also, weights of the references within the multireference calculations were compared. It was shown that use of explicit correlation within the mul- tireference approach, as well as for the single-reference approach, speeds up the convergence of energy by an order when considering the cardinal number of basis set. Keywords: coupled clusters, multireference, explicitly correlated, F12, car- bene 1Katedra fyzikální a makromol. chemieDepartment of Physical and Macromolecular ChemistryPřírodovědecká fakultaFaculty of Scienc
Optimizing quantum simulations and the DMRG method
No full textTitle: Optimizing quantum simulations and the DMRG method Author: Jan Brandejs Department: Department of Chemical Physics and Optics Supervisor: doc. Dr. rer. nat. Jiří Pittner, DSc., J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences Abstract: In this work, we explore the quantum information theoretical aspects of simulation of quantum systems on classical computers, in particular the many- electron strongly correlated wave functions. We describe a way how to reduce the amount of data required for storing the wavefunction by a lossy compression of quantum information. For this purpose, we describe the measures of quantum entanglement for the density matrix renormalization group method. We imple- ment the computation of multi-site generalization of mutual information within the DMRG method and investigate entanglement patterns of strongly correlated chemical systems. We present several ways how to optimize the ground state calculation in the DMRG method. The theoretical conclusions are supported by numerical simulations of the diborane molecule, exhibiting chemically interest- ing electronic structure, like the 3-centered 2-electron bonds. In the theoretical part, we give a brief introduction to the principles of the DMRG method. Then we explain the quantum informational..
Study of Diradicals By Explicitly Correlated Multireference Coupled Cluster Methods
No full textTitle: Study of Diradicals by Explicitly Correlated Multireference Coupled Cluster Methods Author: Matej Švaňa Department: Department of Physical and Macromelecular Chemistry Supervisor: Mgr. Jiří Pittner, Dr. rer. nat., J. Heyrovský Institute of Physical Chemistry Abstract: Total energies of cyclopropane, trimethylene, and propylidene were calculated with conventional post-HF CCSD(T), BWCCSD(T), MkCCSD(T) methods and their explicitly correlated alternatives. Main aims of the the- sis were to compare the basis set convergence of total energies and relative energies between cyclopropane and trimethylene/propylidene, both at the conventional and the explicitly correlated levels. It was shown that use of explicit correlation accelerates the convergence of the total energy by one or- der of basis set quality, resulting in considerable savings in computational times. Also, the MkCCSD(T)-F12/QZ and the BWCCSD(T)-F12/QZ calcula- tions belong to the most sophisticated approaches employed for estimation of the relative energies of cyclopropane and trimethylene/propylidene to date. Keywords: explicitly correlated, coupled cluster, multi-reference, cyclopropane isomerisation, trimethylene, propylidene
[Report to Chief J. E. Curry, by an unknown author #1]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
[Report to Chief J. E. Curry, by an unknown author #2]
No full textReport to Chief J. E. Curry, by an unknown author. The report contains a list of officers who gave depositions to the United States Attorney
Optimizing quantum simulations and the DMRG method
No full textTitle: Optimizing quantum simulations and the DMRG method Author: Jan Brandejs Department: Department of Chemical Physics and Optics Supervisor: doc. Dr. rer. nat. Jiří Pittner, DSc., J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences Abstract: In this work, we explore the quantum information theoretical aspects of simulation of quantum systems on classical computers, in particular the many- electron strongly correlated wave functions. We describe a way how to reduce the amount of data required for storing the wavefunction by a lossy compression of quantum information. For this purpose, we describe the measures of quantum entanglement for the density matrix renormalization group method. We imple- ment the computation of multi-site generalization of mutual information within the DMRG method and investigate entanglement patterns of strongly correlated chemical systems. We present several ways how to optimize the ground state calculation in the DMRG method. The theoretical conclusions are supported by numerical simulations of the diborane molecule, exhibiting chemically interest- ing electronic structure, like the 3-centered 2-electron bonds. In the theoretical part, we give a brief introduction to the principles of the DMRG method. Then we explain the quantum informational..
Parallel Implementation of Multireference Coupled-Cluster Theories Based on the Reference-Level Parallelism
No full textA novel algorithm for implementing a general type of
multireference
coupled-cluster (MRCC) theory based on the Jeziorski–Monkhorst
exponential ansatz [Jeziorski, B.; Monkhorst, H. J. Phys.
Rev. A 1981, 24, 1668] is introduced.
The proposed algorithm utilizes processor groups to calculate the
equations for the MRCC amplitudes. In the basic formulation, each
processor group constructs the equations related to a specific subset
of references. By flexible choice of processor groups and subset of
reference-specific sufficiency conditions designated to a given group,
one can ensure optimum utilization of available computing resources.
The performance of this algorithm is illustrated on the examples of
the Brillouin–Wigner and Mukherjee MRCC methods with singles
and doubles (BW-MRCCSD and Mk-MRCCSD). A significant improvement in
scalability and in reduction of time to solution is reported with
respect to recently reported parallel implementation of the BW-MRCCSD
formalism [Brabec, J.; van Dam, H. J. J.; Kowalski, K.; Pittner, J. Chem. Phys. Lett. 2011, 514, 347]
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