How do you choose a basis set for a Gaussian?

Gaussian basis sets are identified by abbreviations such as N-MPG*. N is the number of Gaussian primitives used for each inner-shell orbital. The hyphen indicates a split-basis set where the valence orbitals are double zeta.

What are basis sets in Gaussian?

A basis set in theoretical and computational chemistry is a set of functions (called basis functions) which are combined in linear combinations (generally as part of a quantum chemical calculation) to create molecular orbitals.

What is def2 TZVP basis set?

def2-TZVPPD – Valence triple-zeta with two sets of polarization functions and a set of diffuse functions. def2-QZVP – Valence quadruple-zeta polarization.

What is 3 21G basis set?

����������� One very economical, small split valence basis set is the 3-21G basis set. The non-valence electrons are described by single basis functions composed of a contraction of three Gaussians. Each valence electron is described by two basis functions.

Which basis set is better?

A significant improvement on 3-21G(*), 6-31G* adds polarization to all (non-hydrogen) atoms, and improves the modeling of core electrons. 6-31G* is often considered the best compromise of speed and accuracy, and is the most commonly used basis set. Available for elements H – Kr.

How do I choose a basis set?

Here, you can choose three different situations.

1. Use different basis set for each atom in order to reduce the calculation time.
2. Use the same basis set for all atom.
3. Use Complete basis set extrapolation (CBS). In my opinion this is one of the best option for high accuracy calculations.

What is HF 3 21G?

The HF/3-21G* basis set was used for the calculations. The Berny analytical gradient method was used for the optimizations. To obtain the final torsional angles of the most stable conformers, calculations of these geometries were performed without constraint on the dihedral angle.

What is Rijcosx?

RI-J for Coulomb integrals and COSX numerical integration for HF exchange. This is called RIJCOSX. RI can also be used for various integral transformations in coupled cluster and CI calculations.

How many basis functions are there in 6 31G?

13 basis functions
A RHF/6-31G(d,p) calculation on water involves 24 basis functions: 13 basis functions for the 6-31G part (just like for 3-21G) plus 3 p-type polarization functions on each H atom and 5 d-type polarization functions (some programs use 6 Cartesian d-functions instead of the usual 5).

What is a primitive Gaussian?

Primitive Gaussian functions. • In the jargon of quantum chemistry a single Gaussian function is called a. primitive Gaussian function, or primitive GTO (Gaussian Type Orbital) • Some programs use Cartesian primitive GTOs: • Other programs use Spherical primitive GTOs.

Who named the different basis sets used in Gaussian software?

6-31G†: Gaussian 16 also includes the 6-31G† and 6-31G‡ basis sets of George Petersson and coworkers, defined as part of various Complete Basis Set methods [Petersson88, Petersson91].

What is a large basis set?

A basis set is a mathematical description of the orbitals within a system used to perform the theoretical calculation. Larger basis sets approximate more accurately the orbitals by imposing fewer restrictions on the locations of the electrons in space.