Welcome to the Website of ACES II !

ACES II (= Advanced Concepts in Electronic Structure) is a series of programs 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.

ACES II offers a number of unique features especially for the accurate calculation of molecular properties.

Particularly noteworthy in this regard are (1) analytic second derivatives for various coupled-cluster models (including CCSD, CCSD(T) and CCSDT) as well as (2) equation-of-motion linear response (EOM-CC/CC-LR) schemes for the investigation of electronically excited, ionized, or electron-attached states. While analytic second derivatives form the basis for either the computation of harmonic and (via additional numerical differentiation) of anharmonic force fiels as well as for electron-correlated prediction of NMR parameters, available analytic derivative schemes for the EOM-CC/CC-LR schemes enable a thorough investigation of excited and/or ionized states. The usefulness of the methodological developments incorporated within the last 15 years in ACES II has been amply demonstrated in numerous publications as well as by the fact that ACES II is routinely used in many research groups all over the world.

However, ACES II is not a commercial code. It is rather a program that is constantly undergoing development; new techniques and improvements are constantly being made (mainly in the groups of John F. Stanton (University of Texas at Austin, USA), Jürgen Gauss (Universität Mainz, Germany), and Peter G. Szalay (Eötvös-Lorand University Budapest, Hungary)). The program is intended to be a research tool, mainly for the developers. However, since the developers strongly feel that others should have access to the program and its many unique features, it has been decided to offer a public version to the academic community free of charge. We hope that, in this way, ACES II (like a few other program packages) might be an important cornerstone for the development of non-commercial quantum chemistry software.


27 April 2009: ACES2 MAB is outdated and replaced by CFOUR