Thermal Vibration Correlation Function Formalism for Molecular Excited State Decay Rates
Authors: Shuai Zhigang 
Published: June 2020

What is the most favorite and original chemistry developed in your research group?

MOMAP, abbreviated for MOlecular MAterials Property prediction package, wherein the key function is the thermal vibration correlation function (TVCF) formalism for excited state decay, allowing theoretical prediction of light‐emitting quantum efficiency and carrier mobility. MOMAP starts to be popular after its first launch in 2015.

How do you get into this specific field? Could you please share some experiences with our readers?

I was trained with theoretical condensed matter physics in Fudan University. At that time, physicists have strong interests in low‐dimensional system because the particular phenomenon has been predicted due to dimensionality. Conducting polymers have been quite a hot topic in the early 80’s since exotic elementary excitations as soliton and polaron have been demonstrated in such systems. Then, the field more and more moved towards theoretical chemistry since the interest in physics was suddenly turned to high Tc superconductivity and fractional quantum Hall effect. My supervisor Prof. Xin Sun and I have kept the interests, ever since the beginning. So, after my PhD in Fudan university, I went to Belgium to work with Prof. Jean‐Luc Bredas, a known theoretical chemist working in the same field. It should be noted that the basic concepts derived from conducting polymers such as spin‐charge separation and fractional charge have been pivotal to understand the novel quantum phenomena such as strongly correlated electrons and topological excitations in novel quantum materials. But the field itself (organic and polymeric optoelectronics) has become interdisciplinary but predominantly chemistry research. And the theory part has expanded the theoretical chemistry scope. So, very naturally, I turned my self to be a theoretical chemist.

How do you supervise your students?

As for theoretical and computational chemistry group, it is imperial to develop their own computational methodology. Nevertheless, applicability is the value of methodology. Namely, the purpose of methodology is to be applied. Thus, it is equally important for the group to do application work, especially, to collaborate with experimental groups by using our own developed methods. So, all my students need to do computational work either to test the applicability of the methodology or to understand the structure‐property for the newly discovered experimental findings, or to clarify some debates in understanding the mechanism/processes. Some of the students have interests in math and physics and in writing program codes. They are stronly encouraged to develop methodology. I am lucky that I do have some excellent students with both motivation and solid math/physics background. I believe they will

do better science than me in the future. And I hope they will also establish their own brand. I will be happy for that. But I am also very happy that the students coming to my group with little theory background but after a few years hard working, they can demonstrate important applications of quantum chemistry and lead to interesting findings by computational study, and they continue their academic career in computational chemistry.

What is the most important personality for scientific research?

Persistence! Chance will come (though only occasionally) to persistent people. Being smart is far from enough.

What's your hobbies? What's your favorite book(s)?

Swimming and music (Rock of the 60s). I like《上帝掷骰子吗?量子物理史话》by曹天元and all the books by Louis Cha (金庸).

How do you keep balance between research and family?

When you are young, say, before 40, you have to work very hard to establish yourself. Sacrificing family life seems inevitable. After that, it is easy to make a balance.

Who influences you mostly in your life?

My high school physics teacher influenced me most. At the time when GaoKao (高考) was not available, there was hardly any serious class education except my physics teacher. Under his guidance, I spent only 6 months to learn and master four years high school curriculum and got into college: in our school that time, less than 2% can get into college, let alone good university as Sun Yet‐sen University. This changed my life.

What is your favorite journal(s)?

The Journal of Chemical Physics, Physical Review B, the Journal of Physical Chemistry (Letters), and more and more, Journal of Chemical Theory and Computation. We theorists usually do not publish or recognize important work in general chemistry journal. Popular is not necessary important, especially for theoretical work. Most of the Nobel Prize works in physical or theoretical chemistry were published in J. Chem. Phys. or Chem. Phys. Lett. (with impact factors around 3).

Could you please give us some advices on improving Chinese Journal of Chemistry?

CJC is a general chemistry journal. Chemistry with broad interest should be the most important priority. Thus, methodology paper is usually of less audience unless it demonstrated broad applicability or possibilities to open new fields of applications.

If you have anything else to tell our readers, please feel free to do so.

Keeping in mind to do different science is the most important thing to do. “First” rather than “better” work is always the top priority.

Excited state decay for complex molecules consists of one of the most challenging issues for theoretical chemistry. By virtue of fast Fourier transformation we developed a highly efficient thermal vibration correlation function formalism for the excited state radiative and non‐radiative decay rates, which transformed the conventional Fermi‐Golden Rule into a time‐dependent formalism and the time‐consuming exponential scaling summation over vibrational states has been converted to an N3 scaling matrix production algorithm combined with time integration. It allows vibration mode mixing (Duschinsky rotation) effect, pertinent for large and soft organic molecules. Another important feature is promoting‐ mode free, rendering this method quite general. By replacing the non‐adiabatic coupling prefactor with intermolecular electronic coupling term, the same formalism can be applied to modeling the carrier mobility in organic semiconductors (which is not discussed in this work). It has been implemented in a portable computational program package MOMAP, which has been successfully applied by many groups for the investigations of organic functional materials, for example, for fluorescent and phosphorescent emission, aggregation induced emission (AIE) phenomena, sensoring process for bilogical and environmental processes, coordinate compounds, thermally activated delayed fluorescence, as well as organic room temperature phosphorescence.