Dr. Sascha Bubeck

Institut für Theoretische Chemie
Greinstraße 4
D50939 Cologne
Germany 
(+49) 221  470  6886 
(+49) 221  470  6896 
sbubeck@smail.unikoeln.de
bubecksascha@tonline.de
About Me
Kindly have a look at my homepage at mkdoku.github.io...
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 functionalbased methods.
One series of PPs, the socalled energyconsistent smallcore 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 frozencore approximation, which introduces an error by neglecting the corecore and, more importantly, the corevalence correlation. One way to describe the majority of these neglected correlations is to use an additional operator in the Hamiltonian, the socalled 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 semiempirical 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 energyconsistent largecore 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 lindependent and ldependent CPP approaches are used, for example for the generation of new energyconsistent 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 HartreeFockSCF simulation and Coupled Cluster simulation using the CPP integrals
 Investigating the influence of the CPP approach in quantum chemical systems
References
Dolg, M. & Cao, X. Relativistic Pseudopotentials: Their Development and Scope of Applications, Chem. Rev. 112, 403480 (2012).↩︎
Dolg, M., Stoll, H. & Preuss, H. Energyadjusted ab initio pseudopotentials for the rare earth elements. J. Chem. Phys. 90, 1730 (1989).↩︎
Dolg, M., Stoll, H., Savin, A. & Preuss, H. Energyadjusted pseudopotentials for the rare earth elements. Theor. Chim. Acta 75, 173194 (1989).↩︎
Küchle, W., Dolg, M. Stoll, H. & Preuss, H. Energyadjusted pseudopotentials for the actinides. Parameter sets and test calculations for thorium and thorium monoxide. J. Chem. Phys. 100, 75357542 (May 1994).↩︎
Cao, X., Dolg, M. & Stoll, H. Valence basis sets for relativistic energyconsistent smallcore lanthanide pseudopotentials. J. Chem. Phys. 118, 487496 (2003).↩︎
Cao, X. & Dolg, M. Segmented contraction scheme for smallcore actinide pseudopotential basis sets. J. Mol. StrucTheochem 673, 203209 (Mar. 2004).↩︎
Dolg, M. & Cao, X. Relativistic Pseudopotentials: Their Development and Scope of Applications, Chem. Rev. 112, 403480 (2012).↩︎
Born, M. & Heisenberg, W. Über den Einfluß der Deformierbarkeit der Ionen auf optische und chemische Konstanten. I Z. Phys 23, 388410 (Dec. 1924).↩︎
Müller, W., Flesch, J. & Meyer, W. Treatment of intershell correlation effects in ab initio calculations by use of core polarization potentials. Method and application to alkali and alkaline earth atoms. J. Chem. Phys. 80, 32973310 (Apr. 1984).↩︎
Müller, W. & Meyer, W. Groundstate properties of alkali dimers and their cations (including the elements Li, Na, and K) from ab initio calculations with effective core polarization potentials. J. Chem. Phys. 80, 3311 (Apr. 1984).↩︎
Fuentealba, P. On the reliability of semi empirical pseudopotentials: dipole polarisability of the alkali atoms. J. Phys. B: At. Mol. Phys. 15 L555L558 (1982).↩︎
Fuentealba, P. Die Rolle der Rumpfpolarisierung in Pseudopotentialverfahren. PhD thesis (1982).↩︎
Fourcrault, M. Millie, P. & Daudey, J. P. Nonperturbative method for corevalence correlation in pseudopotential calculations: Application to the Rb2 and Cs2 molecules. J. Chem. Phys. 96, 12571264 (Jan. 1992).↩︎
Moritz, A., Cao, X. & Dolg, M. Quasirelativistic energyconsistent 5fincore pseudopotentials for divalent and tetravalent actinide elements Theoretical Chemistry Accounts 118, 845854 (June 2007).↩︎
Weigand, A., Cao, X., Yang, J. & Dolg, M. Quasirelativistic fincore pseudopotentials and corepolarization potentials for trivalent actinides and lanthanides: molecular test for trifluorides. Theoretical Chemistry Accounts 126, 117127 (May 2009).↩︎
Weigand, A., Cao, X., Hangele, T. & Dolg, M. Relativistic SmallCore Pseudopotentials for Actinium, Thorium, and Protactinium. J. Phys. Chem A 118 25192530 (2014).↩︎
Weigand, A. Relativistic Energyconsistent Pseudopotentials for fElements. PhD thesis (Universität zu Köln, 2009).↩︎
Souissi, H., Mejrissi, L., Habli, H., AlGhamdi, A. A., Oujia, B. & Gadéa, F. X., Spectroscopic ab initio investigation of the electronic properties of (SrK)^{+}. Chem. Phys. 490, 1928 (June 2017).↩︎
Mtiri, S., Mejrissi, Habli, H., AlGhamdi, A. A., Oujia & Gadéa, F. X. Theoretical investigation of the diatomic Van der Waals systems Ca^{+} and CaHe. Comput. Theor. Chem. 1114, 3346 (Aug. 2017).↩︎