PQS is a general purpose quantum chemistry

Quantum chemistry

Quantum chemistry is a branch of chemistry whose primary focus is the application of quantum mechanics in physical models and experiments of chemical systems...

 program. Its roots go back to the first ab initio gradient program developed in Professor Peter Pulay

Peter Pulay

Peter Pulay is a theoretical chemist. He is the Roger B. Bost Distinguished Professor of Chemistry in the Department of Chemistry and Biochemistry at the University of Arkansas, U.S....

's group but now it is developed and distributed commercially by Parallel Quantum Solutions. There is a reduction in cost for academic users and a site license. Its strong points are geometry optimization, NMR

Nuclear magnetic resonance

Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...

 chemical shift calculations, and large MP2

Møller-Plesset perturbation theory

Møller–Plesset perturbation theory is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...

 calculations, and high parallel efficiency on computing clusters. It includes many other capabilities including Density functional theory

Density functional theory

Density functional theory is a quantum mechanical modelling method used in physics and chemistry to investigate the electronic structure of many-body systems, in particular atoms, molecules, and the condensed phases. With this theory, the properties of a many-electron system can be determined by...

, the semiempirical methods, MINDO

MINDO

MINDO, or Modified Intermediate Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Intermediate Neglect of Differential Overlap method of John Pople. It was developed by the group...

/3, MNDO

MNDO

MNDO, or Modified Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation. Similarly, this method replaced the earlier...

, AM1 and PM3

PM3 (chemistry)

PM3, or Parameterized Model number 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation....

, Molecular mechanics

Molecular mechanics

Molecular mechanics uses Newtonian mechanics to model molecular systems. The potential energy of all systems in molecular mechanics is calculated using force fields...

 using the SYBYL 5.0 Force Field

Force field (chemistry)

In the context of molecular modeling, a force field refers to the form and parameters of mathematical functions used to describe the potential energy of a system of particles . Force field functions and parameter sets are derived from both experimental work and high-level quantum mechanical...

, the quantum mechanics/molecular mechanics mixed method using the ONIOM

ONIOM

The ONIOM is a computational approach developed by Morokuma and co-workers...

 method, Weinhold's Natural Bond Order (NBO) analysis and COSMO solvation model

COSMO Solvation Model

COSMO is the abbreviation for "COnductor-like Screening MOdel", a calculation method for determining the electrostatic interaction of a molecule with a solvent....

s. Recently, highly efficient parallel Coupled Cluster CCSD(T)

Coupled cluster

Coupled cluster is a numerical technique used for describing many-body systems. Its most common use is as one of several quantum chemical post-Hartree–Fock ab initio quantum chemistry methods in the field of computational chemistry...

 code for closed shell systems has been developed. This code includes many other post Hartree-Fock methods: MP2

Møller-Plesset perturbation theory

Møller–Plesset perturbation theory is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...

, MP3

Møller-Plesset perturbation theory

Møller–Plesset perturbation theory is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...

, MP4

Møller-Plesset perturbation theory

Møller–Plesset perturbation theory is one of several quantum chemistry post-Hartree–Fock ab initio methods in the field of computational chemistry...

, CISD

Configuration interaction

Configuration interaction is a post-Hartree–Fock linear variational method for solving the nonrelativistic Schrödinger equation within the Born–Oppenheimer approximation for a quantum chemical multi-electron system. Mathematically, configuration simply describes the linear combination...

, CEPA

CEPA

CEPA may refer to:* Comprehensive Economic Partnership Agreement between India and Republic of Korea. Enforced on 1 January, 2010.* Canadian Environmental Protection Act* Center for Economic Policy Analysis at New School University, New York City...

, QCISD

Quadratic configuration interaction

Quadratic configuration interaction is an extension of Configuration interaction that corrects for size-consistency errors in the all singles and double excitation CI methods ....

and so on.