Quantum chemistry, also called molecular quantum mechanics, is a branch of chemistry focused on the application of quantum mechanics to chemical systems. Understanding electronic structure and molecular dynamics using the Schrödinger equations are central topics in quantum chemistry.
Coupled cluster (CC) is a numerical technique used for describing many-body systems. Its most common use is as one of several post-Hartree–Fock ab initio quantum chemistry methods in the field of computational chemistry, but it is also used in nuclear physics. Coupled cluster essentially takes the basic Hartree–Fock molecular orbital method and constructs multi-electron wavefunctions using the exponential cluster operator to account for electron correlation. Some of the most accurate calculations for small to medium-sized molecules use this method.
Aces II is an ab initio computational chemistry package for performing high-level quantum chemical ab initio calculations. Its major strength is the accurate calculation of atomic and molecular energies as well as properties using many-body techniques such as many-body perturbation theory (MBPT) and, in particular coupled cluster techniques to treat electron correlation. The development of ACES II began in early 1990 in the group of Professor Rodney J. Bartlett at the Quantum Theory Project (QTP) of the University of Florida in Gainesville. There, the need for more efficient codes had been realized and the idea of writing an entirely new program package emerged. During 1990 and 1991 John F. Stanton, Jürgen Gauß, and John D. Watts, all of them at that time postdoctoral researchers in the Bartlett group, supported by a few students, wrote the backbone of what is now known as the ACES II program package. The only parts which were not new coding efforts were the integral packages. The latter was modified extensively for adaptation with Aces II, while the others remained very much in their original forms.
Psi is an ab initio computational chemistry package originally written by the research group of Henry F. Schaefer, III. Utilizing Psi, one can perform a calculation on a molecular system with various kinds of methods such as Hartree-Fock, Post-Hartree–Fock electron correlation methods, and Density functional theory. The program can compute energies, optimize molecular geometries, and compute vibrational frequencies. The major part of the program is written in C++, while Python API is also available, which allows users to perform complex computations or automate tasks easily.
Møller–Plesset perturbation theory (MP) is one of several quantum chemistry post–Hartree–Fock ab initio methods in the field of computational chemistry. It improves on the Hartree–Fock method by adding electron correlation effects by means of Rayleigh–Schrödinger perturbation theory (RS-PT), usually to second (MP2), third (MP3) or fourth (MP4) order. Its main idea was published as early as 1934 by Christian Møller and Milton S. Plesset.
Per-Olov Löwdin was a Swedish physicist, professor at the University of Uppsala from 1960 to 1983, and in parallel at the University of Florida until 1993.
Electronic correlation is the interaction between electrons in the electronic structure of a quantum system. The correlation energy is a measure of how much the movement of one electron is influenced by the presence of all other electrons.
In computational chemistry, post–Hartree–Fock methods are the set of methods developed to improve on the Hartree–Fock (HF), or self-consistent field (SCF) method. They add electron correlation which is a more accurate way of including the repulsions between electrons than in the Hartree–Fock method where repulsions are only averaged.
Quadratic configuration interaction (QCI) is an extension of configuration interaction that corrects for size-consistency errors in single and double excitation CI methods (CISD).
Isaiah Shavitt was a Polish-born Israeli and American theoretical chemist.
In quantum chemistry, size consistency and size extensivity are concepts relating to how the behaviour of quantum chemistry calculations changes with size. Size consistency is a property that guarantees the consistency of the energy behaviour when interaction between the involved molecular system is nullified. Size-extensivity, introduced by Bartlett, is a more mathematically formal characteristic which refers to the correct (linear) scaling of a method with the number of electrons.
Spartan is a molecular modelling and computational chemistry application from Wavefunction. It contains code for molecular mechanics, semi-empirical methods, ab initio models, density functional models, post-Hartree–Fock models, and thermochemical recipes including G3(MP2) and T1. Quantum chemistry calculations in Spartan are powered by Q-Chem.
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term ab initio was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene. The background is described by Parr. Ab initio means "from first principles" or "from the beginning", implying that the only inputs into an ab initio calculation are physical constants. Ab initio quantum chemistry methods attempt to solve the electronic Schrödinger equation given the positions of the nuclei and the number of electrons in order to yield useful information such as electron densities, energies and other properties of the system. The ability to run these calculations has enabled theoretical chemists to solve a range of problems and their importance is highlighted by the awarding of the Nobel prize to John Pople and Walter Kohn.
Josef Paldus, is a Distinguished Professor Emeritus of Applied Mathematics at the University of Waterloo, Ontario, Canada.
Debashis Mukherjee is a theoretical chemist, well known for his research in the fields of molecular many body theory, theoretical spectroscopy, finite temperature non-perturbative many body theories. Mukherjee has been the first to develop and implement a class of many-body methods for electronic structure which are now standard works in the field. These methods, collectively called multireference coupled cluster formalisms, are versatile and powerful methods for predicting with quantitative accuracy the energetics and cross-sections of a vast range of molecular excitations and ionization. A long-standing problem of guaranteeing proper scaling of energy for many electron wave-functions of arbitrary complexity has also been first resolved by him. He has also been the first to develop a rigorously size-extensive state-specific multi-reference coupled cluster formalism, and its perturbative counterpart which is getting increasingly recognized as a very promising methodological advance.
Sourav Pal is an Indian theoretical chemist, a professor of chemistry in IIT Bombay and is the director of the Indian Institute of Science Education and Research Kolkata. Pal is an ex-director of CSIR-National Chemical Laboratory Pune, and adjunct professor at the Indian Institute of Science Education and Research Pune.
Donald Gene Truhlar is an American scientist working in theoretical and computational chemistry and chemical physics with special emphases on quantum mechanics and chemical dynamics.
Piotr Piecuch is a Polish-born American physical chemist. He holds the title of University Distinguished Professor in the Department of Chemistry at Michigan State University, East Lansing, Michigan, United States. He supervises a group, whose research focuses on theoretical and computational chemistry as well as theoretical and computational physics, particularly on the development and applications of many-body methods for accurate quantum calculations for molecular systems and atomic nuclei, including methods based on coupled cluster theory, mathematical methods of chemistry and physics, and theory of intermolecular forces. His group is also responsible for the development of the coupled-cluster computer codes incorporated in the widely used GAMESS (US) package.
Complete active space perturbation theory (CASPTn) is a multireference electron correlation method for computational investigation of molecular systems, especially for those with heavy atoms such as transition metals, lanthanides, and actinides. It can be used, for instance, to describe electronic states of a system, when single reference methods and density functional theory cannot be used, and for heavy atom systems for which quasi-relativistic approaches are not appropriate.
Martin Schütz was a Swiss theoretical chemist and quantum chemist.
