# What is the difference between DFT and TD-DFT in Gaussian 09 software?

• EL AALLAOUI Najla

#### EL AALLAOUI Najla

Homework Statement:: difference between DFT and TDDFT in Gaussian 09 software?
Relevant Equations:: hello , I hope this message finds you well

Please I want to know what is the difference between DFT and time‐dependent density functional theory TD-DFT and why we use it in the measurement of electronic absorption spectra .
Thank you in advance

hello , I hope this message finds you well

Please I want to know what is the difference between DFT and time‐dependent density functional theory TD-DFT and why we use it in the measurement of electronic absorption spectra .
Thank you in advance

EL AALLAOUI Najla said:
Please I want to know what is the difference between DFT and time‐dependent density functional theory TD-DFT and why we use it in the measurement of electronic absorption spectra .
Discrete Fourier Transform? Please link to the reading you have been doing for this question. Thanks.

berkeman said:

Discrete Fourier Transform? Please link to the reading you have been doing for this question. Thanks.
No, Density Functional Theory

vanhees71 and berkeman

## 1. What is DFT in Gaussian 09 software?

DFT stands for Density Functional Theory, which is a computational method used in Gaussian 09 software to calculate the electronic structure of molecules.

## 2. What is TD-DFT in Gaussian 09 software?

TD-DFT stands for Time-Dependent Density Functional Theory, which is an extension of DFT that allows for the calculation of excited states and their properties, such as electronic transitions and absorption spectra.

## 3. What is the main difference between DFT and TD-DFT?

The main difference between DFT and TD-DFT is that DFT is used to calculate the ground state electronic structure of a molecule, while TD-DFT is used to calculate the excited state properties of a molecule.

## 4. Which method should I use for my calculations, DFT or TD-DFT?

The choice between DFT and TD-DFT depends on the specific properties you are interested in calculating. If you are only interested in the ground state electronic structure, DFT is sufficient. However, if you want to calculate excited state properties, TD-DFT is necessary.

## 5. Can DFT and TD-DFT be used together in Gaussian 09 software?

Yes, DFT and TD-DFT can be used together in Gaussian 09 software. In fact, TD-DFT calculations often require the use of DFT calculations as a starting point. The results from DFT calculations are then used to calculate the excited state properties using TD-DFT.