## What is TD-DFT?

Time-dependent density-functional theory (TDDFT) is a quantum mechanical theory used in physics and chemistry to investigate the properties and dynamics of many-body systems in the presence of time-dependent potentials, such as electric or magnetic fields.

**What is TD-DFT in Gaussian?**

The TD-DFT method in Gaussian makes it practical to study excited state systems since it produces results that are comparable in accuracy to ground state DFT calculations. Sometimes, characterizing the specific transition associated with an excited state is straightforward.

**What is the difference between DFT and TD-DFT?**

TD-DFT is the extension of DFT to ES and it originally relies on the theorem published by Runge and Gross in 1984. While DFT can provide, in principle, an exact solution of the time-independent Schrödinger equation, TD-DFT provides the same feat for its time-dependent counterpart.

### What is LR TDDFT?

LR-TDDFT is one way of determining single excitation energies of a molecule from first principles. It is a way of describing how matter interacts with light (or any electromagnetic field). An everyday example is color: sunlight is absorbed by some material, which excites an electron.

**What is Cam B3LYP?**

CAM-B3LYP combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al. CAM-B3LYP yields atomization energies of similar quality to those from B3LYP, while also performing well for charge transfer excitations in a dipeptide model, which B3LYP underestimates enormously.

**What is EOM CCSD?**

EOM-CCSD is an extension of CCSD for modeling excited states. It provides CCSD-level accuracy for excited-state calculations and requires comparable computational cost (scaling as N6 like CCSD) and additional disk space.

## What is density response?

In the specific case of quantum chemistry, the formal solution to this problem is called the density-density response function, which means a linear operator that acts on the perturbation and yields the electronic density response to that perturbation.

**What is the difference between B3LYP and Cam-B3LYP?**

The main difference between the B3LYP and CAM-B3LYP functionals is the amount of exact Hartree-Fock (HF) exchange included.

**What Gaussian 09?**

What is gaussian09? Gaussian is a computer program used by chemists, chemical engineers, biochemists, physicists and other scientists. It utilizes fundamental laws of quantum mechanics to predict energies, molecular structures, spectroscopic data (NMR, IR, UV, etc) and much more advanced calculations.