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Relativistic non-linear optical property calculations with density functional theory

Periodic Reporting for period 1 - RelPro (Relativistic non-linear optical property calculations with density functional theory)

Reporting period: 2017-04-18 to 2019-04-17

The RelPro project had the aim of implementing a computational technique for calculating non-linear optical molecular properties with a relativistic quantum chemistry method. Non-linear optical properties are spectroscopical properties which depend on the intensity of the incident radiation. They are relevant for a large amount of technical applications such as for photochromic materials, frequency conversion of lasers or photodynamic canter therapy. Structure-property relations for these properties are very complex and design of new materials in this field often needs support from computational chemistry.

Relativistic effects are effects originating from the theory of relativity. Most quantum chemical approaches neglect these effects as they render the working equations extremely complex while and their impact on the result is normally very small as long as only lighter element atoms are considered. As heavier atoms come into play, relativistic effects become more and more important it can no longer be neglected. The overall objective of the RelPro project was to provide a fast and reliable computational method which is able to calculate non-linear optical properties for molecular systems including heavy atoms using time-dependent density functional theory (TD-DFT).

During the RelPro project, the fundamental equations for these properties have been derived and a program has been written that is able to calculate first-order hyperpolarizabilities of heavy atom compounds in combination with other quantum chemistry programs.
In the first part of the project, theory work has been performed which had the objective of deriving the relevant working equations. This theory work was challenging as a very accurate and reliable theory approach had been chosen which rendered the fundamental expressions extremely complex. These equations have been fundamental for the implementation of the program realized in the RelPro project. Preliminary results from the project have been shown as a poster on a conference in Halle/Germany and they are part of a publication which has been submitted for review in Physical Chemistry Chemical Physics.
The results from the RelPro preject offer the first fast and reliable opportunity for calculations of non-linear optical properties of heavy atom compounds which has a serious impact on the design of molecules with these properties.