In my research, I use the tools of quantum chemistry to try to determine the properties of molecules as accurately as possible. For this, I develop methods which, for the sake of accuracy, include the so-called electron correlation (Coupled-Cluster and multi-reference type methods), which means that they represent a reliable toolbox that can be systematically improved. Their disadvantage is that they are expensive, so they can only be used for smaller molecules. In applications, I primarily investigate problems in the field of molecular spectroscopy: initially, I performed calculations supporting vibrational spectroscopy, but later - taking advantage of the possibilities provided by electron correlation methods - the study of electron excited states came to the fore. My goal was always to determine very precise results, so my research was mainly limited to small molecules (butadiene, ketenyl radical, ozone, etc.). Thanks to technical progress and the improvement of methods, we can now calculate with increasing precision for larger molecules: in the framework of my current main project, we are investigating the spectroscopic properties of DNA's building blocks (nucleobases, base pairs, etc.) and the mechanism of their charge transfer processes. We are also looking for an answer to the question of whether the DNA molecule conducts electricity. The success of this project shows that the application of high-precision quantum chemical methods is no longer limited to small molecules, but also offers opportunities for biochemical applications.