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

[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

 

[berkeman]

Please define your terms...

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.

 

[DrClaude]

Please define your terms...Discrete Fourier Transform? Please link to the reading you have been doing for this question. Thanks.

No, Density Functional Theory

 

[BAAL144]

In Gaussian 09:

DFT (Density Functional Theory) is used to calculate the ground-state properties of a molecule. It gives information such as:
Optimized geometry
Total energy
HOMO–LUMO energies
Vibrational frequencies
Charge distribution
TDDFT (Time-Dependent Density Functional Theory) is used to calculate the excited-state properties of a molecule. It provides:
Excitation energies
UV–Vis absorption wavelengths
Oscillator strengths
Electronic transitions (e.g., HOMO → LUMO)

In simple words:

DFT tells you how a molecule behaves in its normal (ground) state.
TDDFT tells you what happens when the molecule absorbs light and becomes excited.