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Quantum computing algorithms for quantum chemistry
Višňák, Jakub ; Skála, Lubomír (advisor) ; Čurík, Roman (referee) ; Pittner, Jiří (referee)
Title: Quantum computing algorithms for quantum chemistry Author: Jakub Višňák Abstract: The topic of this study is the simulation of the quantum algorithm for the diagonalization of the matrix representation of the all-electron Dirac-Coulomb hamiltonian of the SbH molecule. Two different limited CI expansions were used to describe both the ground state (X 0+ ) and the first excited doublet (A 1) by simulating the Iterative Phase Estinamtion Algorith (IPEA). In the simulations numerically performed in this work, the "compact mapping" has been employed for the representation of the evolution operator exp(i Hˆ t); in the theoretical part of the work, the "direct mapping" is described as well. The influence of the metodics for choosing the initial eigenvector estimate is studied in both IPEA A and IPEA B variants. For those variants, the success probabilities pm are computed for different single-points on the SbH dissociation curves. The initial eigenvector estimates based on the "CISD(2)" method are found to be sufficient for both studied LCI-expansions up to internuclear distance R 6 a0. The pm dependence on the overlap between the eigenvector in question and its inital estimate - 2 0 is studied the for IPEA B method. The usability of the both variants of the IPEA in possible later calculations is...
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Parallel Implementation of Multireference Coupled Clusters Methods and Calculations on Large Systems
Brabec, Jiří ; Pittner, Jiří (advisor) ; Fišer, Jiří (referee) ; Pitoňák, Michal (referee)
Firstly, we have developed a Tensor Contraction Engine-based implementation of the BW-MRCCSD approach. The scalability tests have been performed across thousand of cores. We have further developed a novel two-level parallel algorithm for Hilbert-space MRCC methods which uses the processor groups. In this approach, references are distributed among processor groups (reference-level parallelism) and tasks of each reference are distributed inside of a given processor group (task-level parallelism). We have shown that our implementation scales across 24000 cores. The usability of our code was demonstrated on larger systems (dodecane, polycarbenes and naphthyne isomers). Finally, we present novel universal state- selective (USS) corrections to the state-specific MRCC methods. The USS-corrected MRCC results were compared with the full configuration interaction (FCI) results.
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Structure and dynamics of electronic defects in liquid water
Maršálek, Ondřej ; Jungwirth, Pavel (advisor) ; Horáček, Jiří (referee) ; Pittner, Jiří (referee)
Title: Structure and dynamics of electronic defects in liquid water Author: Ondřej Maršálek Institute: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic Supervisor: prof. Mgr. Pavel Jungwirth, DSc. Supervisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: In this thesis we present ab inito molecular dynamics simulations of two different electronic defects in water. Photoionization of liquid water produces a cationic hole, which undergoes ultrafast dynamics and forms the hydrated proton and the hydroxyl radical as its products. We study both the dynamics and spectroscopy of this process. The hydrated electron is a key intermediate in radiation chemistry of aqueous systems. We simulate its equilibrium properties in anionic water clusters as well as the dynamics of vertical electron attachment to cold and warm clusters. The hydrated electron reacts with a hydrated proton to form a hydrogen atom. We examine this reaction at a finite temperature in a larger cluster as well as in more detail in a smaller cluster. Because both of the electronic defects studied here are challenging open-shell species, we put emphasis on benchmarking and testing our computational setup. Six published articles are attached to the thesis. Keywords: density functional theory,...
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Multireference CC calculations using optimized virtual orbitals
Lang, Jakub ; Pittner, Jiří (advisor) ; Uhlík, Filip (referee)
i Abstract The aim of this work is to test the performance of multireference methods using the truncated virtual orbital space as a result when OVOS method is employed. As a guess function, the OVOS wave function is used for the calculations of the two-determinantal state of a quasi-degenerate system. The resulting energies are investigated for different truncation of the virtual orbital space.
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Explicitly correlated multireference coupled cluster computations
Švaňa, Matej ; Pittner, Jiří (advisor) ; Nachtigall, Petr (referee)
Title: 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 1
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Multireference State-Specific Mukherjee's Coupled Cluster Method with Non-iterative Triexcitations.
Bhaskaran Nair, Kiran ; Pittner, Jiří (advisor) ; Noga, Jozef (referee) ; Fišer, Jiří (referee)
The multireference (MR) generalization of coupled cluster (CC) theory aims to describe both the static and the dynamic correlation accurately, as the standard CC method (at lower truncation levels) generally does not perform well when quasidegenerate boundary orbitals are encountered. The most promising among the MR Hilbert-space methods seems to be the state-specific MR Mukherjee's CC (MkCC) method, formulated by Mukherjee et al. [J. Chem. Phys. 110, 6171 (1999)], due to its rigorous size-extensivity and insensitivity to the intruder state problem. The main goal of this work was to include connected triples in the MkCC method. As the cost of the iterative triples limits its application, the main focus was on including triples non-iteratively. Two perturbative triples methods, namely MkCCSD(Tn) and MkCCSD(Tu) have thus been developed. For studying their accuracy, iterative triples methods (MkCCSDT and MkCCSDT-n) were also developed using the "linked" formulation. All these methods and an uncoupled version of MkCC (uMkCC) were implemented in the ACES II program. The assessment of these methods was performed on the O2, cyclobutadiene, methylene diradical, twisted ethylene, F2, BeH2 and tetramethyleneethane (TME) molecules. All these studies show that the inclusion of triexcitations improves the...
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