Search

With this preface we are happy to present volume 77 of the Advances in Quantum Chemistry to our readers. In the present volume we portray a varied set of dishes of scientific accomplishments, which we hope will be both stimulating and provoke discussion. The tray begins with general topics in Life Sciences and Medicine, and continues with fundamental applications of Aromatic Maps, followed by considering more exact treatments of quantum systems, like accurate few particle calculations, determinations of relativistic ionization cross sections, and then via quantum control of optical frequency combs to the admittance of endohedral confinement, non-Hermitian descriptions of electron-molecule resonances and finally in the development of spheroidal coordinates for Coulomb Sturmians for the speed-up of molecular calculations. The introductory article concerns an added celebration of the scientific leadership of Per-Olov Löwdin, see the AQC Löwdin Memorial Volume, issue 74 for original contributions. The author, a student “getting lost” in the research organizations of high-tech world-wide industries like Sandvik AB, and IBM, did not abandon the field as he later joined the IBM Almaden Research in San Jose as their Director of Quantum Chemistry. Through his lead involvement in the IBM-Roche collaboration he developed growing concerns regarding Life Sciences and Medicine, which upon retirement encouraged him to found his own company, while writing a highly praised book on nano-technology. The second chapter continues the Life Science theme with a fundamental delving into the topic of the origin of life. Using quantum entanglement algorithms for duplex RNA genome systems, interesting replacement repair enzymes outline entanglement-enabled bases for e.g. age-related disorders, like Huntington’s-, Alzheimers’ decease etc. After these two chapters there follows an up-to-date and detailed review of electron-atom collision processes, including relativistic effects, with particula

All mean excitations energies for second and third row atoms and their ions are calculated in the random‐phase approximation using large basis sets. To a very good approximation it turns out that mean excitation energies within an isoelectronic series is a quadratic function of the nuclear charge. It is demonstrated that this behavior is linked to the fact that the contributions from continuum electronic states give the dominate contributions to the mean excitation energies and that these contributions for atomic ions appear hydrogen‐like. We argue that this finding may present a method to get a first estimate of mean excitation energies also for other non‐relativistic atomic ions.

Calculations of the continuum contributions to dipole oscillator sum rules for hydrogen are performed using both exact and basis-set representations of the stick spectra of the continuum wave function. We show that the same results are obtained for the sum rules in both cases, but that the convergence towards the final results with increasing excitation energies included in the sum over states is slower in the basis-set cases when we use the best basis. We argue also that this conclusion most likely holds also for larger atoms or molecules.

The essential material constant that determines the bulk of the stopping power of high energy projectiles, the mean excitation energy, is calculated for a range of smaller molecular ions using the RPA method. It is demonstrated that the mean excitation energy of both molecules and atoms increase with ionic charge. However, while the mean excitation energies of atoms also increase with atomic number, the opposite is the case for mean excitation energies for molecules and molecular ions. The origin of these effects is explained by considering the spectral representation of the excited state contributing to the mean excitation energy.

A method for calculation of the mean excitation energies of atomic ions is presented, making the calculation of the energy deposition of fast ions to plasmas, warm, dense matter, and complex biological systems possible. Results are reported to all ions of helium, lithium, carbon, neon, aluminum, and argon.

Using an asymmetric-Lanczos-chain algorithm for the calculation of the coupled cluster linear response functions at the CCSD and CC2 levels of approximation, we have calculated the mean excitation energies of the noble gases He, Ne and Ar, and of the hydrogen molecule H2. Convergence with respect to the one-electron basis set was investigated in details for families of correlation consistent basis sets including both augmentation and core-valence functions. We nd that the electron correlation effects at the CCSD level change the mean excitation energies obtained at the uncorrelated Hartree-Fock level by about 1%. For the two-electron systems He and H2, our CCSD results (for a Lanczos chain length equal to the full excitation space), I0 = 42:28 eV (Helium) and I0 = 19:62 eV (H2), correspond to full conguration interaction results and are therefore the exact, non-relativistic theoretical values for the mean excitation energy of these two systems within the Bethe theory for the chosen basis set and, in the case of H2, at the experimental equilibrium geometry.