# What is the difference between quantum espresso and VASP?

## What is the difference between quantum espresso and VASP?

VASP is a commercial code and Quantum-Espresso (QE) is an open source code. Both have their own issues: For calculations of vibrational properties, QE contains implementations of DFPT (Density Functional Perturbations Theory), whereas VASP uses another third party software.

### What is difference between VASP and Gaussian?

Gaussian is the main quantum chemistry DFT code, so it probably is about equivalent to VASP, but with a local basis instead of a planewave one. This means you have to make decisions about the basis functions and you may have a harder time with solids. Gaussian also costs money.

**How do you find the dipole moment in Gaussian?**

The dipole moment in Gaussian is defined with respect to the center of positive charge. However, if your molecule is neutral changing the origin for defining the dipole moment does not change the dipole moment itself. If your system is charged then changing the origin from R1 to R2 will change the dipole by (R1-R2)q.

**What is TD DFT 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 DFT software?

Quantum chemistry computer programs are used in computational chemistry to implement the methods of quantum chemistry. They may also include density functional theory (DFT), molecular mechanics or semi-empirical quantum chemistry methods. The programs include both open source and commercial software.

### How do you find the dipole moment of a bond?

A dipole moment is the product of the magnitude of the charge and the distance between the centers of the positive and negative charges. It is denoted by the Greek letter ‘µ’. It is measured in Debye units denoted by ‘D’. 1 D = 3.33564 × 10-30 C.m, where C is Coulomb and m denotes a meter.

**What is RMS gradient norm?**

The RMS gradient is the root mean squared gradient, sqrt( mean( F_i dot. F_i ) ), where F_i is the force on atom i and mean() takes an average. over all atoms.

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

As per my opinion, DFT is used for ground state geometry optimization and TD-DFT is used for excited state geometry optimization and other theoretical calculations. To get more clear idea you may follow the computational details of my publication, Chemical Physics Letters 634 (2015) 29–36.

## Is Gaussian software free?

this program is for paid and can not get it free.

### What is DFT modeling?

Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases.