Last Updated: 06/08/2015

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Introduction to p2-RDM | Downloading p2-RDM | Using p2-RDM | Feedback

The parametric two-electron reduced density matrix (2-RDM) method is a novel technique in electronic structure theory in which both the ground-state energy and 2-RDM of a many-electron atom or molecule are directly computed. The basic variable of many-electron quantum mechanics is typically chosen to be the N-electron wave function where N is the number of electrons in the quantum system. In 2-RDM methods, however, the 2-RDM of an atom or molecule is directly computed rather than the N-electron wave function. The 2-RDM must be constrained by nontrivial conditions to ensure that it represents an N-electron density matrix. Such constraints are known as N-representability conditions. In the parametric 2-RDM method, the 2-RDM is parameterized in terms of its lowest order components. Applications of the parametric methods have been made to computing the energetic stability of oxywater, the relative energies of the cis and trans isomers of carbonic acid, the rotational barrier between the cis and trans isomers of diazene, and the stability of olympicene and its isomers.

- The p2-RDM method is especially useful in treating moderate multi-reference electron correlation as occurs in bond dissociation, transition states, and diradicals.
- It yields energies that generally lie between those from coupled cluster singles-doubles (CCSD) and those from CCSD with triples (CCSDT).
- The p2-RDM ensures that the energy is nearly size extensive and that the 2-RDM is nearly N-representable.
- It has a computational cost equal to that of CISD and hence, less than that of CCSD.
- The code fully exploits a molecule's Abelian point-group symmetry for both computational speed and memory efficiency.

- D. A. Mazziotti, Phys. Rev. Lett. 101, 253002 (2008)
- D. A. Mazziotti, Phys. Rev. A. 81, 062515 (2010)
- C. A. Schwerdtfeger, A. E. DePrince III, and D. A. Mazziotti, J. Chem. Phys. 134, 174102 (2011)

If you would like to install a copy of the code on your computer, please send your name, your mailing address, your intended use (a short sentence or two), and your computer architecture in an e-mail to David Mazziotti (rdmchem@gmail.com).

A manual is available with the code.

Please address feedback about the programs or theory to David Mazziotti (rdmchem@gmail.com).

We are open to suggestions, extensions, and collaborations on application projects.

-David Mazziotti