30 research outputs found
New Approaches for ab initio Calculations of Molecules with Strong Electron Correlation
Reliable quantum chemical methods for the description of molecules with
dense-lying frontier orbitals are needed in the context of many chemical
compounds and reactions. Here, we review developments that led to our
newcomputational toolbo x which implements the quantum chemical density matrix
renormalization group in a second-generation algorithm. We present an overview
of the different components of this toolbox.Comment: 19 pages, 1 tabl
A Quantum Computing Implementation of Nuclear-Electronic Orbital (NEO) Theory: Towards an Exact pre-Born-Oppenheimer Formulation of Molecular Quantum Systems
Nuclear quantum phenomena beyond the Born-Oppenheimer approximation are known
to play an important role in a growing number of chemical and biological
processes. While there exists no unique consensus on a rigorous and efficient
implementation of coupled electron-nuclear quantum dynamics, it is recognised
that these problems scale exponentially with system size on classical
processors and therefore may benefit from quantum computing implementations.
Here, we introduce a methodology for the efficient quantum treatment of the
electron-nuclear problem on near-term quantum computers, based upon the
Nuclear-Electronic Orbital (NEO) approach. We generalize the electronic
two-qubit tapering scheme to include nuclei by exploiting symmetries inherent
in the NEO framework; thereby reducing the hamiltonian dimension, number of
qubits, gates, and measurements needed for calculations. We also develop
parameter transfer and initialisation techniques, which improve convergence
behavior relative to conventional initialisation. These techniques are applied
to H and malonaldehyde for which results agree with Nuclear-Electronic
Orbital Full Configuration Interaction and Nuclear-Electronic Orbital Complete
Active Space Configuration Interaction benchmarks for ground state energy to
within Ha and entanglement entropy to within . These
implementations therefore significantly reduce resource requirements for full
quantum simulations of molecules on near-term quantum devices while maintaining
high accuracy.Comment: 26 pages, 7 figures, 10 table
Quantum chemical calculations of X-ray emission spectroscopy
The calculation of X-ray emission spectroscopy with equation of motion coupled cluster theory (EOM-CCSD), time dependent density functional theory (TDDFT) and resolution of the identity single excitation configuration interaction with second order perturbation theory (RI-CIS(D)) is studied. These methods can be applied to calculate X-ray emission transitions by using a reference determinant with a core-hole, and they provide a convenient approach to compute the X-ray emission spectroscopy of large systems since all of the required states can be obtained within a single calculation removing the need to perform a separate calculation for each state. For all of the methods, basis sets with the inclusion of additional basis functions to describe core orbitals are necessary, particularly when studying transitions involving the 1s or- bitals of heavier nuclei. EOM-CCSD predicts accurate transition energies when compared with experiment, however, its application to larger systems is restricted by its computational cost and difficulty in converging the CCSD equations for a core-hole reference determinant, which become increasing problematic as the size of the system studied increases. While RI-CIS(D) gives accurate transition energies for small molecules containing first row nuclei, its application to larger systems is limited by the CIS states providing a poor zeroth order reference for perturbation theory which leads to very large errors in the computed transition energies for some states. TDDFT with standard exchange-correlation functionals predicts transition energies that are much larger than experiment. Optimization of a hybrid and short-range cor- rected functional to predict the X-ray emission transitions results in much closer agreement with EOM-CCSD. The most accurate exchange-correlation functional identified is a modified B3LYP hybrid functional with 66% Hartree-Fock exchange, denoted B66LYP, which predicts X-ray emission spectra for a range of molecules including fluorobenzene, nitrobenzene, ace- tone, dimethyl sulfoxide and CF3Cl in good agreement with experiment
Crowdfunding in Russia
Tato bakalářské práce se zabývá crowdfundingem, moderním způsobem získání potřebného množství finančních prostředků za účelem realizace vlastních a podnikatelských záměrů. Cílem této práce je podívat se na crowdfundingový trh Ruska, který není na území České republiky příliš znám. První část práce stručně popisuje tradiční způsoby financování začátku podnikání. Druhá část popisuje teoretickou náplň crowdfundingu od vysvětlení pojmu až po jeho celosvětový vývoj v posledních letech. Třetí část se zabývá analýzou ruského crowdfundingové trhu a jeho současným stavem.The bachelor thesis is concerned about crowdfunding – the modern way of gaining sufficient amount of financial sources for realization of own or business ideas. Its goal is to describe the current situation on Russian crowdfunding market, which is quite unknown market for Czech audience. The first part of the thesis briefly describes more tradition ways for financial sources seeker. The second one provides with information about theoretical base of crowdfunding from definition till world market dynamics. The third one analyzes Russian crowdfunding market and its current situatio
Analytical gradients for excitation energies from frozen-density embedding
The formulation of analytical excitation-energy gradients from time-dependent density functional theory within the frozen-density embedding framework is presented. In addition to a comprehensive mathematical derivation, we discuss details of the numerical implementation in the Slater-function based Amsterdam Density Functional (ADF) program. Particular emphasis is put on the consistency in the use of approximations for the evaluation of second- and third-order non-additive kinetic-energy and exchange–correlation functional derivatives appearing in the final expression for the excitation-energy gradient. We test the implementation for different chemical systems in which molecular excited-state potential-energy curves are affected by another subsystem. It is demonstrated that the analytical implementation for the evaluation of excitation-energy gradients yields results in close agreement with data from numerical differentiation. In addition, we show that our analytical results are numerically more stable and thus preferable over the numerical ones.ISSN:1463-9084ISSN:1463-907