Peter A. Limacher

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The polarizability and second hyperpolarizability of polyacetylene oligomer chains of increasing size up to C(24)H(26) were investigated by means of the Coulomb-attenuating method (CAM-B3LYP) using response theory. It was found that this long-range corrected density functional removes to large parts the overestimation observed for standard methods and in(More)
The chemistry encyclopedia Römpp Online and the German universal encyclopedia Wikipedia were assessed by first-year university students on the basis of a set of 30 articles about chemical thermodynamics. Criteria with regard to both content and form were applied in the comparison; 619 ratings (48% participation rate) were returned. While both encyclopedias(More)
We have implemented the sweep algorithm for the variational optimization of SU(2) U(1) (spin and particle number) invariant matrix product states (MPS) for general spin and particle number invariant fermionic Hamiltonians. This class includes non-relativistic quantum chemical systems within the Born-Oppenheimer approximation. High-accuracy ab initio finite(More)
In this study, we present a scheme for the evaluation of electron delocalization and conjugation efficiency in lineraly π-conjugated systems. The scheme, based on the natural bond orbital theory, allows monitoring the evolution of electron delocalization along an extended conjugation path as well as its response to chemical modification. The scheme(More)
The finite field method, widely used for the calculation of static dipole polarizabilities or the first and second hyperpolarizabilities of molecules and polymers, is thoroughly explored. The application of different field strengths and the impact on the precision of the calculations were investigated. Borders could be defined and characterized,(More)
In this article, we report on the ab initio calculation of the static longitudinal second hyperpolarizability (γ) of π conjugated unsaturated oligomer chains using polyacetylene and polyyne as model compounds. The common observation is that the electron correlation enhances γ in these systems. The present study reveals that for extended chain lengths the(More)
A new truncation scheme for non-orthogonal antisymmetrized products of interacting geminals (APIG) is introduced based on antisymmetrized products of strongly orthogonal geminals (APSG). This wavefunction hierarchy of interacting geminals (IG) allows us to gradually increase the accuracy at which the ground state of a seniority-zero Hamiltonian can be(More)
To understand better the impact of donor-acceptor substitution on the properties of linearly π-conjugated compounds, we performed a computational study on a series of variably substituted trans-polyacetylenes, polyynes, and polythiophenes. The focus of this work is on how rapidly the impact of a given substituent or a given combination of substituents(More)
Intermolecular binding between a Hamilton wedge and cyanuric acid, a frequently employed binding motif to achieve self-assembly of single-chain polymer nanoparticles, is studied by means of ab initio quantum-chemical and DFT calculations. A conformational analysis of the isolated compounds and the hydrogen-bonded complex reveals several low-energy(More)
As part of a systematic study of the impact of donor-acceptor substitution on the structure and properties of pi-conjugated compounds, we present a theoretical investigation of the all-trans polyacetylene backbone, end-capped with moieties of different donor or acceptor natures and different strengths, focusing on the effects induced by these substituents(More)