My current primary research area is concerned with singlet fission in photovoltaics. In this case, we are performing high level multireference computations in order to elucidate the nature of the states present.
In addition to that I am involved in several other areas in organic electronics:

thiophene based molecules with potential for OLED applications [10, 33],

(p-phenylene vinylene) oligomers with applications in photovoltaics [11,25,28],

open-shell character in graphene nanoribbons of various types [9,17, 30, 35],

methodological aspects of iridium complex excited states [22], and

dynamics of ultrafast charge separation [36].

Dynamics of electronic defects in DNA and model systems

My PhD project was devoted to the dynamics of electronic defects (excess charges or excitation energy) between several molecules.
In particular we were investigating the photophysics and charge transfer properties of DNA and the influence stacking and base pairing has on this. For reviews of computations on these systems, consider Refs [4, 15, 34].

Our first project was concerned with charge transfer in stacked π-systems.
The ethylene dimer radical cation with a bridge of up to three formaldehyde molecules proved to be an excellent model system to examine the basic physics of charge transfer.[3] Based on this experience a more extended study of energy transfer and proton-coupled electron transfer in the 2-pyridone dimer radical cation was performed.[8]

The remaining project was concerned with the description of actual nucleic acid fragments. First, The UV absorbing states in alternating DNA duplexes were described, where a particular focus was laid on the description of excitonic and CT interactions.[7] For this purpose an analysis strategy based on the one-electron transition density matrix was devised, implemented and tested on several interesting systems.[6] Finally, exciplex formation in the adenine dinucleotede was examined.[13]

Excited state intramolecular proton transfer (ESIPT)

My diploma thesis was concerned with excited state double proton transfer in the [2,2'-Bipyridyl]-3,3'-diol molecule. Here it was of specific interest to understand the mechanistic details of this ultrafast sub-picosecond process. In particular we pointed out that the process should occur in a sequential fashion.[1,2] Additionally I have been involved in studies on some other molecules exhibiting ultrafast ESIPT.[5]

Program development

TheoDORE

The TheoDORE (Theoretical Density, Orbital Relaxation, and Exciton) analysis package is a diverse and flexible wavefunction analysis suite.
Aside from different population analysis methods and the natural transition orbital decomposition, special features of TheoDORE are concerned with

electron-hole correlation plots to visualize static correlation in the excited state [6],

natural difference orbitals showing orbital relaxation [18, 19],

computation of an approximate exciton size [21, 24],

an entanglement analysis [31], and

the analysis of unpaired electrons [9].

libwfa

The wavefunction analysis library libwfa is a parallel development to TheoDORE, allowing to do wavefunction analysis in an integrated fashion. The main enhancments as compared to TheoDORE are

multipole analysis of exciton wavefunctions to allow the computation of exciton sizes and correlation coefficients [21, 24],

exciton binding energies (in progress),

an entanglement analysis [31], and

enhanced plotting capabilities.

Feel free to contact me or another developer if you are interested in interfacing libwfa to a quantum chemical code.

COLUMBUS

COLUMBUS is an ab-initio electronic structure package, focused on multi-reference methods. My involvement includes

Improving the efficiency of parallel MR-CI calculations with a special focus on non-adiabatic dynamics simulations.

Maintaining and expanding the interface to the MOLCAS code [27].

Controlling the work-flow in parallel MR-CI calculations to allow for user-friendly utilization of the newly devoloped program code. For applications see Refs [9, 14].

Enhancing the efficiency of the computation of gradients and non-adiabatic couplings at the state averaged multi-configuration self-consistent field method to allow for non-adiabatic dynamics simulations of systems of signficantly increased size. In particular the computation of the non Hellmann-Feynman terms has been sped up.

Interfacing of different modules to allow for an efficient calculation of spin-orbit coupling elements to be used for non-adiabatic dynamics simulations.[20]

Providing an efficient and flexible way to interface to the various functionalities of COLUMBUS, in particular in connection with dynamics simulations and QM/MM hybrid treatment (through work on the runc execution script and the colinp interactive input facility). In particular I am working on some of the input tools to speed up user input without losing flexibility in the input options.

Aside from providing functionality it is a particular concern of mine also to have high user friendliness. For this purpose I modified some of the input scripts for automatization. Additionally I tried to improve the understandability of some common error messages. If you have any suggestions in this context, please write me (Contact).

MOLCAS

MOLCAS is an ab-initio quantum chemistry package, which allows performing multiconfigurational computations across the periodic table [27]. My work is concerned with

Maintaining and expanding the interface to the COLUMBUS program package [27]

Implementation of new wavefunction analysis methods through the wavefunction analysis library libwfa

Q-CHEM

Q-CHEM is a comprehensive ab-initio quantum chemistry package with a wide range of electronic structure methods implemented. My current work is concerned with excited state analysis methods within the algebraic diagrammatic construction (ADC) of the polarization propagator including

Density matrix based analysis and visualization methods implemented for the ADC method [18,19] providing deeper insight into excited state structure including an analysis of the transition density matrix for the visualization of electron-hole correlations [6, 24] and an attachment/detachment density analysis

The same analysis for time-dependent density functional theory calculations with a focus on dynamic charge transfer effects [26]

NEWTON-X

NEWTON-X is a modular program system which performs non-adiabatic dynamics simulations in connection with different electronic structure programs.[12] My work includes

Implementation of local diabatization a stable way of integrating the time-dependent electronic Schrödinger equation.[8]

ADC(2) non-adiabatic couplings and general maintenance of the wavefunction overlap code.[16]

Normal mode analysis and Essential Dynamics to be able to follow and analyze molecular motions. For more details see my Diploma Thesis (Sec. 2.3.4), for applications consider Refs [2,8].

Interface to COLUMBUS 7.0.

You are welcome to contact me if you have any questions with respect to these topics.

SHARC

SHARC (Surface Hopping including Arbitrary Couplings) is a software suite used for the simulation of non-adiabatic molecular dynamics.
Aside from standard photodynamics, it allows for the simulation of intersystem crossing and explicit interactions with a radiation field.
My work is concerned with

The efficient computation of wavefunction overlaps as needed for non-adiabatic dynamics simulations [29].

Personal projects

The molecular structure manipulation toolkit is intended to allow easy access to some common structure manipulation tasks (see Downloads).

The wave function analysis tools are written to facilitate different tasks in analyzing
wave functions and molecular orbitals. This work has culminated in producing the TheoDORE package (see above).

MSc Thesis:"Dynamics simulation of excited state intramolecular proton transfer" (Link)

PhD Thesis:"Quantum Mechanical Simulations of Defect
Dynamics in DNA and Model Systems" (Link)

Publication list

If you need a reprint of one of these papers, feel free to contact me.

-- 2017 --

[39] Das, A.; Müller, T.; Plasser, F.; Krisiloff, D.; Carter, E.; Lischka, H."Local Electron Correlation Treatment in Extended Multireference Calculations: Effect of Acceptor-Donor Substituents on the Biradical Character of the Polyaromatic Hydrocarbon Heptazethrene"J. Chem. Theory Comput.2017, x, x.
DOI: 10.1021/acs.jctc.7b00156

[38] Chopra, S.; Plasser, F."Excited state analysis of absorption process in metal decorated Boron nitride nanoribbons"2017, x, x.
DOI: 10.1080/00268976.2017.1324646

[37] Mewes, S. A.; Plasser, F.; Dreuw, A."Universal Exciton Size in Organic Polymers is Determined by Non-Local Orbital Exchange in TDDFT"J. Phys. Chem. Lett.2017, 8, 1205.
DOI: 10.1021/acs.jpclett.7b00157

[36] Wiebeler, C.; Plasser, F.; Hedley, G.; Ruseckas, A.; Samuel, I.; Schumacher, S.
"Ultrafast Electronic Energy Transfer in an Orthogonal Molecular Dyad"J. Phys. Chem. Lett.2017, 8, 1086.
DOI: 10.1021/acs.jpclett.7b00089

[35] Luzanov, A.; Plasser, F.; Das, A.; Lischka, H."Evaluation of the quasi correlated tight-binding (QCTB) model
for describing polyradical character in polycyclic hydrocarbons"J. Chem. Phys.2017, 146, 064106.
DOI: 10.1063/1.4975196

[34] Marquetand, P.; Nogueira, J. J.; Mai, S.; Plasser, F.; González, L."Challenges in Simulating Light-Induced Processes in DNA"Molecules2017, 22, 49.
DOI: 10.3390/molecules22010049

[33] Holzer, B.; Bintinger, J.; Lumpi, D.; Choi, C.; Kim, Y.;
Stöger, B.; Hametner, C.; Marchetti-Deschmann, M.; Plasser, F.; Horkel, E.; Kymissis, I.; Fröhlich, J.
"Color Fine Tuning of Optical Materials Through Rational Design"ChemPhysChem2017, 18, 549.
DOI: 10.1002/cphc.201601204

-- 2016 --

[32] Plasser, F.; González, L."Communication: Unambiguous comparison of many-electron wavefunctions through their overlaps"J. Chem. Phys.2016, 145, 021103.
DOI: 10.1063/1.4958462

[30] Das, A.; Müller, T.; Plasser, F.; Lischka, H."The Polyradical Character of Triangular non-Kekulé Structures, Zethrenes, p-Quinodimethane Linked Bisphenalenyl and the Clar Goblet in Comparison: An Extended Multireference Study"J. Phys. Chem. A2016, 120, 1625.
DOI: 10.1021/acs.jpca.5b12393

[29] Plasser, F.; Ruckenbauer, M.; Mai, S.; Oppel, M.; Marquetand, P.; González, L."Efficient and Flexible Computation of Many-Electron Wavefunction Overlaps"J. Chem. Theory Comput.2016, 12, 1207.
DOI: 10.1021/acs.jctc.5b01148

[28] Mewes, S. A.; Mewes, J.-M.; Dreuw, A.; Plasser, F."Excitons in poly(para phenylene vinylene): A quantum-chemical perspective based on high-level ab initio calculations"Phys. Chem. Chem. Phys.2016, 18, 2548.
DOI: 10.1039/C5CP07077E

[27] F. Aquilante et al."Molcas 8: New Capabilities for Multiconfigurational Quantum Chemical Calculations across the Periodic Table"J. Comp. Chem.2016, 37, 506.
DOI: 10.1002/jcc.24221

-- 2015 --

[26] Mewes, S. A.; Plasser, F.; Dreuw, A."Communication: Exciton analysis in time-dependent density functional theory: How functionals shape excited-state characters"J. Chem. Phys.2015, 143, 171101.
DOI: 10.1063/1.4935178

[25] Kraner, S.; Scholz, R.; Plasser, F.; Koerner, C.; Leo, K."Exciton size and binding energy limitations in one-dimensional organic materials"J. Chem. Phys.2015, 143, 244905.
DOI: 10.1063/1.4938527

[24] Plasser, F.; Thomitzni, B.; Bäppler, S. A.; Wenzel, J.; Rehn, D. R.; Wormit, M.; Dreuw, A."Statistical analyis of Electronic Excitation Processes: Spatial Location, Compactness, Charge Transfer, and Electron-Hole Correlation"J. Comp. Chem2015, 36, 1609.
DOI: 10.1002/jcc.23975

[23] Georgieva, I. M.; Aquino, A. J. A.; Plasser, F.; Trendafilova, N.; Köhn, A.; Lischka, H."Intramolecular Charge Transfer Excited State Processes in 4-(N,N-Dimethylamino)benzonitrile: The Role of Twisting and the πσ* State"J. Phys. Chem. A2015, 119, 6232.
DOI: 10.1021/acs.jpca.5b03282

[22] Plasser, F.; Dreuw, A."High-Level Ab Initio Computations of the Absorption Spectra of Organic Iridium Complexes"J. Phys. Chem. A2015, 119, 1023.
DOI: 10.1021/jp5122917

[15] Plasser, F.; Aquino, A. J. A.; Lischka, H.; Nachtigallova, D."Electronic Excitation Processes in Single-Strand and Double-Strand DNA: A Computational Approach."Top. Curr. Chem.2015, 356, 1.
DOI: 10.1007/128_2013_517

-- 2014 --

[21] Bäppler, S. A.; Plasser, F.; Wormit, M.; Dreuw, A."Exciton analysis of many-body wavefunctions: Bridging the gap between the quasi-particle and molecular orbital pictures"Phys. Rev. A2014, 90, 052521.
DOI: 10.1103/PhysRevA.90.052521

[20]
Müller, T; Mai, S.; Plasser, F.; Marquetand, P.; Lischka, H.; Gonzalez, L."Perturbational treatment of spin-orbit coupling for generally applicable high-level multi-reference methods"J. Chem. Phys.2014, 141, 074105.
DOI: 10.1063/1.4892060

[19] Plasser, F.; Bäppler, S. A.; Wormit, M.; Dreuw, A."New tools for the systematic analysis and visualization of electronic excitations. Part II: Applications"J. Chem. Phys.2014, 141, 024107.
DOI: 10.1063/1.4885820

[18] Plasser, F.; Wormit, M.; Dreuw, A."New tools for the systematic analysis and visualization of electronic excitations. Part I: Formalism"J. Chem. Phys.2014, 141, 024106.
DOI: 10.1063/1.4885819

[17]
Horn, S.; Plasser, F.; Müller, T.; Libisch, F.; Burgdörfer, J. Lischka, H."A comparison of singlet and triplet states for one- and two-dimensional graphene nanoribbons using multireference theory"Theor. Chem. Acc.2014, 133, 1511.
DOI: 10.1007/s00214-014-1511-8

[16] Plasser, F.; Crespo-Otero, R.; Pederzoli, M.; Pittner, J.; Lischka, H.; Barbatti, M."Surface Hopping Dynamics with Correlated Single-Reference Methods: 9H-Adenine as a Case Study"J. Chem. Theo. Comp.2014, 10, 1395.
DOI: 10.1021/ct4011079

[14] Cui, Zhong-hua; Lischka, H.; Müller, T.; Plasser, F.; Kertesz, M. "Study of the diradicaloid character in a prototypical pancake bonded dimer: the stacked tetracyanoethylene (TCNE) anion dimer and the neutral K_{2}TCNE_{2} complex"ChemPhysChem2014, 15, 165.
DOI: 10.1002/cphc.201300784

[12] Barbatti, M.; Ruckenbauer, M.; Plasser, F.; Pittner, J.; Granucci, G.; Persico, M.; Lischka, H. "NEWTON-X: a surface-hopping program for nonadiabatic molecular dynamics"WIREs Comp. Mol. Sci.2014, 4, 26. DOI: 10.1002/wcms.1158

-- 2013 --

[13] Plasser, F.; Lischka, H."Electronic Excitation and Structural Relaxation of the Adenine Dinucleotide in Gas Phase and Solution"Photochem. Photobiol. Sci.2013, 12, 1440. DOI: 10.1039/C3PP50032B

[11] Panda, A.; Plasser, F.; Aquino, A. J. A.; Burghardt, I.; Lischka, H."Electronically Excited States in Poly(p-phenylene vinylene): Vertical Excitations and Torsional Potentials from High-level Ab Initio Calculations"J. Phys. Chem. A2013, 117, 2181. DOI: 10.1021/jp400372t

[9] Plasser, F.; Pasalic, H.; Gerzabek, M. H.; Libisch, F.; Reiter, R.; Burgdörfer, J.; Mueller, T.; Shepard, R.; Lischka, H."The Multiradical Character of One- and Two-Dimensional Graphene Nanoribbons"Angew. Chem., Int. Ed.2013, 52, 2581. DOI: 10.1002/anie.201207671

-- 2012 --

[8] Plasser, F.; Granucci, G.; Pittner, J.; Barbatti, M.; Persico, M.; Lischka, H."Surface hopping dynamics using a locally diabatic formalism: charge transfer in the
ethylene dimer cation and excited state dynamics in the 2-pyridone dimer"J. Chem. Phys.2012, 137, 22A514. DOI: 10.1063/1.4738960

[7] Plasser, F.; Aquino, A.J.A.; Hase, W.L.; Lischka, H."UV absorption spectrum of alternating DNA duplexes. Analysis of excitonic and charge transfer interactions"J. Phys. Chem. A2012, 116, 11151. DOI: 10.1021/jp304725r

[6] Plasser, F.; Lischka, H."Analysis of excitonic and charge transfer interactions from quantum chemical calculations"J. Chem. Theo. Comp.2012, 8, 2777. DOI: 10.1021/ct300307c

[5] Kungwan, N.; Plasser, F.; Aquino, A. J. A.; Barbatti, M.; Wolschann, P.; Lischka, H."The effect of hydrogen bonding on the excited-state proton transfer in 2-(2'-hydroxyphenyl)benzothiazole: a TDDFT molecular dynamics study"
Phys. Chem. Chem. Phys.2012, 14, 9016-9025. DOI: 10.1039/C2CP23905A

[4] Plasser, F.; Barbatti, M.; Aquino, A.J.A.; Lischka, H."Electronically excited states and photodynamics: a continuing
challenge"Theor Chem Acc2012, 131, 1073. DOI: 10.1007/s00214-011-1073-y

-- 2011 --

[3] Plasser, F.; Lischka, H."Semiclassical dynamics simulations of charge transport in stacked π-systems"J. Chem. Phys.2011, 134, 034309. DOI: 10.1063/1.3526697

-- 2009 --

[2] Plasser, F.; Barbatti, M.; Aquino, A. J. A.; Lischka, H."Excited-State Diproton Transfer in [2,2'-Bipyridyl]-3,3'-diol: the Mechanism Is Sequential,
Not Concerted"J. Phys. Chem. A2009, 113, 8490-8499. DOI: 10.1021/jp9032172 [full text]

[1] Aquino, A. J. A.; Plasser, F.; Barbatti, M.; Lischka, H."Ultrafast Excited-state Proton Transfer Processes: Energy Surfaces and
On-the-fly Dynamics Simulations"Croat. Chem. Acta2009, 82, 105-114.

Talks

12 April 2017

"Excited State Wavefunction Analysis: From Practical Tools to Esoteric Effects"