Thursday, April 23, 2026

DFT Functionals

DFT Functionals – Concept, Categories, and Detailed Study

Why Functionals Are Used in DFT

In Density Functional Theory, the total electronic energy of a system is written as:

Introduction to Density Functional Theory (DFT)

Introduction to Density Functional Theory (DFT)

1. Introduction

In computational chemistry, we use quantum mechanics and computer simulations to study molecules and materials. One of the most powerful and widely used methods is Density Functional Theory (DFT).

Vibrational Analysis (IR Spectroscopy from DFT)

Vibrational Analysis (IR Spectroscopy from DFT)

“After optimizing a molecule using DFT, how do we know the structure is correct and stable?”

Then say:

“We verify it using vibrational analysis and compare with IR spectra.”

What is Vibrational Analysis?

Definition:

Vibrational analysis studies how atoms in a molecule move (vibrate) around their equilibrium positions.

Time-Dependent Density Functional Theory

Time-Dependent Density Functional Theory (TD-DFT)

“What does DFT calculate — ground state or excited state?”

Answer: Ground state

Then say:

But what happens when a molecule absorbs light?
An electron gets excited.
DFT cannot properly describe this — so we need TD-DFT.

Basis Sets

Basis Sets in Quantum Chemistry

HF, MP2, and CC are methods used for how to calculate energy

Now the question is

With what mathematical tools do we represent orbitals? That tool is called Basis Sets

Detail study of Hartree Fock and its assumptions

Hartree–Fock (HF) Method

Scientists asked:

“How can we simplify the many-electron problem?”

Replace complex interactions with an average field. This is the Hartree–Fock idea.

Main Assumption

Each electron moves in the average field of all other electrons instead of tracking exact electron–electron motion.