Dr. Andreas Götz: Projects
Building the Computational Tools for Scientific DiscovieriesMy research interests lie in the field of high performance computing (HPC) and large scale scientific computing with a particular emphasis on problems of relevance for (bio)chemistry and nanotechnology. I am developing highly parallel algorithms and software implementations to enable new predictive computational science through quantum mechanical (QM) and classical atomistic numerical simulations on well established and emerging HPC platforms including graphics processing units (GPUs). The majority of my developments are implemented into the ADF software package for density functional theory (DFT) and the AMBER software package for classical and mixed quantum/classical molecular dynamics (MD) simulations which are both used by a large number of academic and industrial researchers world wide.
jump to: Workshops - QM/MM - Subsystem DFT - OEP and TDDFT - Density Fitting (PhD) - Work camp
Workshops
AMBER workshop at ECNU in Shanghai (August 2011)
I am organizer and instructor of an AMBER workshop at East China Normal University (ECNU) in Shanghai. This five day workshop (22-26 August, 2011) aims to introduce researchers in the field of (bio)molecular simulations to the broad collection of computational tools implemented in the AMBER and AmberTools software packages for molecular dynamics simulations.
ADF workshop at SDSC (March 2011)
Together with Dr. Matt Kundrat from SCM I have organized and tutored an ADF workshop that was held on Thursday, 24 March 2011 at the San Diego Supercomputer Center. The workshop was geared both at begineers and expert users of ADF wishing to learn about the new features of the ADF2010.02 release.
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QM/MM for Biomolecular Simulations
Postdoc in San Diego with Dr. R. Walker (June 2009 - June 2011)
Information will be added soon.
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Subsystem Density Functional Theory
Postdoc in Amsterdam with Dr. L. Visscher (November 2006 - April 2009)
I have been and still continue to work on the extension of the frozen density embedding (FDE) method in density functional theory (DFT). The main research topics are analytical gradients for FDE and nuclear spin-spin coupling constants in the framework of FDE. The research work is done with Dr. L. Visscher at the chair of theoretical chemistry at the Vrije Universiteit Amsterdam which is headed by Prof. Dr. E.-J. Baerends.
DFT is undoubtedly the most popular computational method for the investigation of the electronic structure of molecules. It allows to obtain accurate information on molecular properties at a moderate computational cost. Studies of molecules of interest for classic organic or inorganic chemistry are routine by now. It is the time to find new approaches to be able to study also more complex systems in fields of increasing importance such as life sciences and nanotechnology.
The extension of FDE to a general subsystem DFT has a tremendous potential as an accurate (in principle exact) multi-scale modelling method. Such methods allow to focus the computational effort on those parts of the system which is of importance for the property of interest, while still taking into account the interaction with the remaining parts of the system. Proper implementations will allow to tackle the investigation of properties of chemical systems of unprecedented size and complexity. The implementation is done in the Amsterdam Density Functional (ADF) program package.
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Optimized Effective Potential Method and Time-dependent Density Functional Theory
Postdoc in Erlangen with Prof. Dr. A. Görling (October 2005 - October 2006)
Conventional density functional theory (DFT) methods like those based on the local density approximation (LDA) or generalized gradient approximations (GGAs) employ approximate functionals for the exchange-correlation (XC) energy that are integrals of functions of the electron density and its gradient. GGA methods are widely and successfully employed routine methods to investigate electronic ground states and their properties in chemistry and solid state physics. Despite their success, these conventional DFT methods are not accurate enough for many questions of interest.
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In recent years, a new generation of DFT methods emerged that uses functionals that not only depend on the elctron density and its gradients but also on Kohn-Sham orbitals. These DFT methods require the solution of the optimized effective potential (OEP) equations which are plagued by numerical stability problems if localized basis sets are employed. Together with Dr. A. Heßelmann I have developed a numerically stable approach which can be used for ground state calculations with orbital-dependent functionals [1,2]. Our method has been implemented and tested for exact-exchange (EXX) DFT which employs the exact exchange functional instead of approximations to it. Time-dependent density functional theory (TD-DFT) is a very efficient and in many cases encouragingly accurate method to describe electronically excited states of molecules. A fundamental problem which has not yet been solved concerns excited states with charge-transfer (CT) character. Such excited states, which are of importance for a great deal of applications, cannot be described by GGA XC functionals. A very promising avenue to solve this problem is the extension of the EXX approach to excited states [3]. Although the theory has been worked out already in 1998, no practical implementation for molecules exists so far. |
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Based on our numerically stable OEP approach I have worked out algorithms and implemented these into the TD-DFT module of the quantum chemical program package TURBOMOLE. Research along these lines is further pursued in Prof. Dr. A. Görling's group.
[1] A. Heßelmann, A. W. Götz, F. Della Salla, A. Görling, J. Chem. Phys. 127, 054102 (2007).
[2] A. Görling, A. Ipatov, A. W. Götz, A. Heßelmann, Z. Phys. Chem. 224, 325-342 (2010).
[3] A. Görling, Int. J. Quant. Chem. 69, 265-277 (1998).
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Density Fitting Approaches for Efficient Density Functional Calculations
PhD thesis, Erlangen, Germany (November 2001 - August 2005)
My PhD thesis in Theoretical Chemistry was accomplished at the University of Erlangen under the supervision of Prof. Dr. B. A. Heß (University of Bonn, deceased) and later under the supervision of Prof. Dr. A. Görling. I have been working on the LEDO-DFT [1] formalism and its implementation into the quantum chemical program package TURBOMOLE. LEDO-DFT speeds up density functional theory (DFT) calculations and thus enables simulations of larger molecules.
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LEDO is an acronym for limited expansion of diatomic overlap densities and is a novel density fitting approach to speed up molecular DFT calculations. Conventional density fitting methods (also called RI methods) as generally employed in DFT expand the complete electron density into a fit basis which is distributed over the whole system (molecule). As a result one- to three-center two-electron repulsion integrals (ERIs) have to be evaluated and the computational expense is O(N3) with respect to the size N of the system under investigation as compared to O(N4) for conventional DFT. In the LEDO-DFT formalism each individual diatomic overlap density is expanded into a fit basis which is restricted to the atoms of that overlap density. Thus, two-center matrix elements of the Coulomb- and Exchange-Correlation contribution to the Kohn-Sham matrix can be expressed in terms of the one-center elements using the LEDO expansion coefficients. Consequently only one- and two-center ERIs have to be evaluated and the computational expense of the Kohn-Sham matrix formation in a LEDO-DFT calculation is reduced to O(N2). |
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During my PhD I have implemented the calculation of analytical gradients [2] within the LEDO-DFT formalism [1]. Furthermore, I have worked out criteria for the optimization of auxiliary basis sets for the LEDO expansion and optimized auxiliary orbitals which allow for LEDO-DFT calculations with sufficient accuracy [3].
My PhD thesis can be downloaded in pdf format from the opus server of the University of Erlangen.
diploma thesis, Erlangen, Germany (April 2001 - October 2001)My diploma thesis was accomplished during the time from April to October 2001 under the supervision of Prof. Dr. B. A. Heß (University of Bonn, deceased) at the University of Erlangen. It is entitled Implementierung eines vereinfachten Dichtefunktionalverfahrens (Implementation of a Simplified Density Functional Formalism) and deals with the implementation of the LEDO-DFT[1] formalism (see PhD thesis) in the SCF part of the DFT programs of the quantum chemical program package TURBOMOLE.
My diploma thesis (available only in German) can be download here: ps / pdf
[1] C. Kollmar, B. A. Hess, Molec. Phys. 100, 1945-1955 (2002).
[2] A. W. Götz, C. Kollmar, B. A. Hess, Molec. Phys. 103, 175-182 (2005).
[3] A. W. Götz, C. Kollmar, B. A. Hess, J. Comput. Chem. 26, 1242-1253 (2005).
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Renovating a Monastery in Northern Italy (back to top)
Work camp in Àcqui Terme, Italy (September 1995)
In September 1995, after finishing school and before university started, I participated in a workcamp organized by SCI (Service Civil International). It took place in a small village near Àcqui Terme which is close to the town of Asti in the Piemont region in northern Italy.
The philosohpy of the workcamps organized by SCI is to bring together the working and/or creative power of people from different countries in order to realize a project of social welfare. In general the participants have to pay the trip to the workcamp by themselves, but board and lodging at the working place are for free. In my case the project of the work camp was to renovate the run-down accomodations of a small protestant church for future use as a cost-free excursion center for schools or other institutions or people in need. We have been a dozen people from Great Britain, the Netherlands, Germany and Italy. It was hard work, but also a lot of fun.
The duration of the workcamp was two weeks, rather short. Nevertheless it was a unique and worthy experience. If you have time, I can just recommend to participate in a workcamp organized by SCI.
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last modification: 2011/07/02