Quantum Chemistry Group
Quantum chemistry is about theoretical predicting of structure and properties of atoms and molecules. The fundamental equation that governs behavior of electrons – the Schroedinger equation – is far too complex to be solved exactly for real systems. Thus, quantum chemistry relies on approximate methods that, ideally, yield accurate results at bearable computational cost (“bearable” in practice may mean a few seconds or weeks). A continuous progress in this field is possible due to development of novel more accurate and more efficient computational methods. They find applications for example in characterizing and explaining properties of known molecules, designing new materials of desired properties, or in investigating mechanisms of chemical reactions. The field of application is endless but proper computational tools have to be at hand.
Manyelectron methods can be roughly divided into those that aim at solving the Schroedinger equation by assuming a certain mathematical form for a wavefunction (think of the HartreeFock or the coupled cluster methods) and those that do not involve a wavefunction explicitly but employ less complex and easier to handle by computers functions (the most prominent example of such an approach is DFT – density functional theory – a workhorse of today’s computational chemistry).
We are developing quantum chemistry theories and methods applicable to investigate electronic structure of atoms and molecules that employ reduced density matrices or electron densities. In particular, our fields of interest include:
Oneelectron Reduced Density Matrix Methods
We pursue the idea of replacing the wavefunction by reduced density matrices and developing methods for ground and excited state description of molecules. In the last few years we have been working on density matrix functional theory (RDMFT) and its timedependent variant (TDRDMFT) [13].
Rangeseparation methods
We also work towards exploiting the idea of rangeseparating electronelectron interaction into the short and longrange regimes in predicting excited electronic states of molecules. We have proposed a theory that allows one to combine longrange density matrix functionals or longrange wavefunction methods with shortrange density functionals within a linear response theory. This offers a possibility of predicting excitations unavailable in standard approaches to a widely used TDDFT method [45].
Density functional methods development
Conventional density functional approximate functionals show unsatisfactory performance when applied to molecular interaction. We have proposed a DFT based method capable of describing accurately molecular interactions of different nature. The method is based on a dispersionless functional and is applicable to predicting interaction energy of two noncovalently bonded subsystems [6].
We are also interested in developing density functional methods for computing excited state energies of molecules by using variational approaches. For this purpose we employ statistical ensemble variational principle [7].
[1] O. Gritsenko, K. Pernal, and E.J. Baerends, Journal of Chemical Physics, 122 (2005) 204102; “An improved density matrix functional by physically motivated repulsive corrections”.
[2] K. Pernal, O. Gritsenko, and E.J. Baerends, Physical Review A, 75 (2007) 012506; “Timedependent densitymatrixfunctional theory”.
[3] K. Chatterjee and K. Pernal, Journal of Chemical Physics, 137 (2012) 204109; “Excitation energies from extended random phase approximation employed with approximate one and twoelectron reduced density matrices”.
[4] D.R. Rohr, J. Toulouse, and K. Pernal, Physical Review A, 82 (2010) 052502; “Combining density functional theory and densitymatrixfunctional theory”.
[5] K. Pernal, Journal of Chemical Physics, 136 (2012) 184105; “Excitation energies from rangeseparated timedependent density and density matrix functional theory”.
[6] K. Pernal, R. Podeszwa, K. Patkowski, and K. Szalewicz, Physical Review Letters, 103 (2009) 263201; “Dispersionless Density Functional Theory”.
[7] E. Pastorczak, N. I. Gidopoulos, and K. Pernal, Physical Review A, 87 (2013) 0625501; „Calculation of electronic excited states of molecules using the Helmholtz freeenergy minimum principle”.
Group Leader
Group Projects
A PhD position is available.
Recent Publications

M. Matoušek, K. Pernal, F. Pavošević, L. Veis, Variational Quantum Eigensolver Boosted by Adiabatic Connection, J. Phys. Chem. A 128(3), 687698, 2024

R. Zuzak, M. Kumar, O. Stoica, D. Soler‐Polo, J. Brabec, K. Pernal, L. Veis, R. Blieck, A. M. Echavarren, P. Jelínek, S. Godlewski, On‐Surface Synthesis and Determination of the Open‐Shell Singlet Ground State of Tridecacene**, January 2024

D. Drwal, M. Matoušek, P. Golub, A. Tucholska, M. Hapka, J. Brabec, L. Veis, K. Pernal, Role of Spin Polarization and Dynamic Correlation in Singlet–Triplet Gap Inversion of Heptazine Derivatives, J. Chem. Theory Comput., 2023

D. Cieśliński, A. Tucholska, M. Modrzejewski, PostKohn–Sham RandomPhase Approximation and Correction Terms in the ExpectationValue CoupledCluster Formulation, J. Chem. Theory Comput. 19(19), 66196631, 2023

M. Hapka, A. KrzemińskaKowalska, M. Modrzejewski, M. Przybytek, K. Pernal, Efficient Calculation of the Dispersion Energy for Multireference Systems with Cholesky Decomposition: Application to ExcitedState Interactions, J. Phys. Chem. Lett., 68956903, 2023