About Me

Hi!

My name is Sascha Bubeck (he/him) and I work as a software engineer at BioSolveIT. I obtained my PhD in Theoretical Chemistry at the University of Cologne (See ‘Research Interests’ below) and joined BioSolveIT in the beginning of 2022.

Welcome to my homepage, which I use to document my process of deepening my knowledge of programming languages and their respective ecosystems. While I mainly use C++ and the Qt framework for my work at BioSolveIT, I eager to use more functional-oriented languages, like Haskell and Elm, during my leisure time. Only if there are more fitting to my problems, of course.

Research Interests

Quantum Chemistry

Simulating chemical systems is the major goal in quantum chemistry. Over the last decades, the advances in computer technology and quantum chemical approaches opened up new possibilities for simulating increasingly larger systems. Computational demands, however, rapidly increase with the size of the system to be simulated. Thus, approximations are required for reducing these demands. Especially the simulation of systems containing heavy atoms is computationally demanding due to the large number of electrons present in such systems. Relativistic effects, which are pronounced in these systems and therefore have to be taken into account, further increase the computational demand.

Effective Core Potentials (Master Thesis)

One approach, which incorporates relativistic effects and reduces computational demands for heavy atoms, is the use of effective core potentials (ECPs) ¹. ECPs, of which pseudopotentials (PPs) are a subclass, are suitable for application in various quantum chemical approaches, both for wave function- and density functional-based methods.

One series of PPs, the so-called energy-consistent small-core PPs, were previously generated by M. Dolg et al. for the lanthanide ^{2 3} and actinide elements ^{4 5 6} and are used for the majority of simulations of compounds containing these elements.

My master thesis project was focused on the generation of improved PPs of this type for some of the lanthanide elements.

Core Polarization Potentials (PhD Thesis)

ECPs employ the frozen-core approximation, which introduces an error by neglecting the core-core and, more importantly, the core-valence correlation. One way to describe the majority of these neglected correlations is to use an additional operator in the Hamiltonian, the so-called core polarization potential (CPP) operator ⁷.

This idea dates back to Born and Heisenberg, who corrected their calculated Potassium spectra by accounting for the contribution of the core dipole polarizability ⁸. After this first semi-empirical application of the CPP operator, Meyer et al. derived the first general theory and applied it to the first molecular systems ^{9 10}. This approach was later used during the generation of energy-consistent large-core PPs for the alkaline elements by Fuentalba et al. ^{11 12}. The method was then refined by Daudey et al., who extended the CPP by a projection operator on the spherical harmonics, making the CPPs dependent on the angular momentum ¹³. Nowadays, both the l-independent and l-dependent CPP approaches are used, for example for the generation of new energy-consistent di-, tri- and tetravalent PPs by Weigand and Dolg ^{14 15 16 17} or for the simulation of collision experiments by Gadea et al.^{18 19}. Despite the broad use of the CPP operator in simulations of chemical systems, a systematic investigation of its influence on atomic and molecular properties is still lacking.

Goals of the PhD Thesis:

• Implementation of CPP routine for generating and using CPP integrals in quantum chemical simulations into QOL
• Implementation of interface between Hartree-Fock-SCF simulation and Coupled Cluster simulation using the CPP integrals
• Investigating the influence of the CPP approach in quantum chemical systems

References