Research Output per year

## Personal profile

### Research

My research can be subdivided in three major themes that are briefly discussed below.

### 1. Subsystem Methods based on Density Functional Theory

In this programme we develop and apply subsystem approaches that connect various quantum and classical mechanical methods. Using density functional theory (DFT) as unifying theory, we work on methods in which local electronic properties are calculated with accurate coupled cluster methods while the electronic structure of the environment is treated using a DFT or approximate DFT approach. This not only speeds up calculations by orders of magnitudes but also keeps a local picture that facilitates the transfer of results to model hamiltonian approaches. This enables multiscale approaches to the modeling of complex systems for a wide range of research fields; examples are enzymatic catalysis, virtual screening of pharmaceutically active compouds and light harvesting, in which respectively reaction rates, binding affinities, and excitonic couplings are input for models used at higher length and time scales.

### 2. Reducing the time-to-solution of computational models

In this line of research I work closely with the in-house SCM company and computer scientists to improve upon the speed and numerical accuracy of DFT-based modeling. We have recently extended our python-based scripting environment for multiscale computational workflows to automatically exploit parallelism. This enables use of the relatively cheap resources available in computational grids.

To shorten the time spent in indivdual calculations we furthermore collaborate with Oak Ridge National Laboratory to develop algorithms that scale up to the thousands of processor core available in the next generation supercomputers. This is combined with the development of algorithms suitable for GPU-accelaration as they are found in both supercomputers as well as in desktop computers.

An exciting new research line in this field concerns the investigation of quantum chemistry algorithms that can be run on quantum computers. Here we consider composite methods in which an otherwise intractable electron correlation problem can be solved using a quantum computer, while the another part of the calculation is done using a conventional computer.

### 3. Development and application of relativistic computational chemistry techniques

Standard quantum chemistry techniques are not suited for high precision calculations on molecules containing heavy elements because the strong electrostatic potential in the vicinity of the nuclei accelerates the electrons to velocities that approach the speed of light. The Dirac relativistic quantum theory of Dirac describes this high-velocity regime properly and can thus be used to develop a more general quantum chemical framework. In a long-standing European collaboration we work on development of relativistic methods with a focus on methods that allow for accurate treatment of electron correlation effects. In collaboration with users of our DIRAC program system I thereby worked on a wide range of topics (metrology, quantum computing, nuclear quadrupole moments, main group metal clusters) for which the use of highly accurate electronic structure methods is crucial. In my own group I mostly focused on applications to actinide chemistry, a field that has only just become accessible for accurate quantumchemical modeling. We are now able to achieve chemical accuracy by use of multireference coupled cluster techniques based on a relativistic Hamiltonian. With our development of efficient algorithms and advances in computer technology it is nowadays possible to study realistic systems and we collaborate with applied theoretical groups (in the US, Germany and France) to study various aspects of actinide chemistry.

### Ancillary activities

No ancillary activities

*Ancillary activities are updated daily*

### Education

1978-1984 VWO – Rijksscholengemeenschap Meppel

1984-1989 Master (drs.) in Chemistry – Rijks Universiteit Groningen (RuG)

1989-1993 Doctorate in Science – RuG

Thesis: Relativity and Electron Correlation in Chemistry

Promotor: Prof Dr W. C. Nieuwpoort

Date and judicium: September 10, 1993 *cum laude*

### Prizes and Awards

1996: Clemens Roothaan award, KNCV

2005: Vici, NWO

2006: Dirac Medal, World Association of Theoretical Chemists

2010: Wiley Visiting Scientist, Pacific Northwest National Laboratory

### Teaching

### Bachelor level

Introdction to Scientific Programming (2017-present)

Thermodynamics (2012-present)

Introduction to Chemistry (2015-2017)

Molecular Quantum Mechanics (2010-2012)

Nuclear Chemistry (2010-2012)

Programming for Chemists (2004-2012)

Inorganic Chemistry (2006-2010)

Chemical Bonding (1998-2003)

### Master level

Understanding Quantum Chemistry (1998-present)

Relativistic Quantum Chemistry (1998-present)

Advanced Molecular Quantum Mechanics (2011-present)

Scientific Computing and Programming (2009-present)

Quantum Theory of Molecules and Matter (2008-2012)

### Postdoctoral level (Summer and Winterschools)

European School in Quantum Chemistry, Palermo (2005-present)

Actinide Chemistry, Helsinki (2007).

Giambiagi Winterschool, Buenos Aires (2006).

ACTINET school in Theoretical Actinide Chemistry, Lille (2006)

Theoretical Chemistry, Mariapfarr (2004).

Theory and Spectroscopy, Han-Sur-Lesse (Belgium), (1999, 2011, 2016)

Determination of Nuclear Quadrupole Moments, Helsinki (1996).

### Education/Academic qualification

PhD, University of Groningen

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Network
Recent external collaboration on country level. Dive into details by clicking on the dots.

## Research Output 1991 2018

## Approximations in Density Functional Based Excited State Calculations

Rüger, R. 2018 115 p.Research output: Thesis › PhD Thesis - Research VU, graduation VU

## Four-Component Polarization Propagator Calculations of Electron Excitations: Spectroscopic Implications of Spin-Orbit Coupling Effects

Pernpointner, M., Visscher, L. & Trofimov, A. B. 13 Mar 2018 In : Journal of Chemical Theory and Computation. 14, 3, p. 1510-1522 13 p.Research output: Contribution to journal › Article

## Regional Susceptibility in VCD Spectra to Dynamic Molecular Motions: The Case of a Benzyl α-Hydroxysilane

Xia, Y., Koenis, M. A. J., Collados, J. F., Ortiz, P., Harutyunyan, S. R., Visscher, L., Buma, W. J. & Nicu, V. P. 5 Mar 2018 In : ChemPhysChem. 19, 5, p. 561-565 5 p.Research output: Contribution to journal › Article

## Correction to Efficient Calculation of Electronic Absorption Spectra by Means of Intensity-Selected Time-Dependent Density Functional Tight Binding

Ruger, R., van Lenthe, E., Lu, Y., Frenzel, J., Heine, T. & Visscher, L. 11 Jul 2017 In : Journal of Chemical Theory and Computation. 13, 7, p. 3424-3425 2 p.Research output: Contribution to journal › Article

## Coulomb couplings in solubilised light harvesting complex II (LHCII): challenging the ideal dipole approximation from TDDFT calculations

Lopez-Tarifa, P., Liguori, N., van den Heuvel, N., Croce, R. & Visscher, L. 28 Jul 2017 In : Physical Chemistry Chemical Physics - PCCP. 19, 28, p. 18311-18320Research output: Contribution to journal › Article