## Density Corrected-Density Functional Theory (DC-DFT)

In the early days of DFT, non-self-consistent Kohn-Sham energy was often evaluated upon Hartree-Fock (HF) densities as a way to test new approximations. This method was called HF-DFT.

It has been discovered that in some cases, HF-DFT actually gave more accurate answers when compared to self-consistent DFT calculations. By using our scheme(Ref), we found that DFT calculations can be categorized into two different types of calculations. First we decompose the error of an approximate functional into two parts: error from the functional (functional error), and error from the density (density-driven error).

For most calculations, functional error is dominant, and here self-consistent DFT is usually better than non-self consistent DFT on more accurate densities (which we call density corrected DFT (DC-DFT)). Unlike these 'normal' calculations, there is a class of calculations where the density-driven error is much larger, so DC-DFT give better a result than self-consistent DFT . We classify these calculations as 'abnormal'. HF-DFT is a simple implementation of DC-DFT and we found that a small HOMO-LUMO gap is an indicator of abnormal calculation, thus, HF-DFT would perform better in such cases.

We tried to determine which are abnormal cases among well-known problematic cases in DFT, and applying DC-DFT to solve these challenging problems.

Theoretical and Computational Chemistry

If you choose important things for chemistry,

1. Create New Material – Synthetic Chemistry

2. Characterize Property of those Material – Analytical Chemistry

3. Reveal the Principle of Property – Physical Chemistry

etc.

Theoretical physical chemistry is a field to explain changes of various systems’ structures, physical & chemical properties, and chemical reactions based on physical principles.

Recent trend in theoretical physical chemistry is to present the basis for creating new materials through the creation of knowledge that can explain and predict the nature of the system, as well as to obtain more direct and specific knowledge by mimicking the structure and movement of the system. This trend stems from the influence of the continuous advancement of fast and large memory capacity of computers.

Due to the development of computers, it is now possible to perform necessary calculations which applied theories of quantum mechanics, classical mechanics, and statistical mechanics, which collectively describe the properties of many particles, such as atoms and molecules, and quantum mechanics, which describe systems in electronic units quickly and accurately. The field of research that identifies the properties of substances using computers is called computational chemistry or computational chemistry.

This field is the most rapidly developing field in recent years, and its importance and scope of application are expanding day by day, having a great influence on all fields of chemistry and neighboring fields such as physics, astronomy, biology, medicine, pharmacy, and material science.

Each computational chemistry lab adopts suitable calculation methods according to the complexity of the system to be calculated. In this laboratory, the following three fields are selected.

PI: Path Integral

MD: Molecular Dynamics

QM: Quantum Mechanics