The most accurate electronic structure methods based on N-particle wave functions are too expensive to be applied to large systems. It is clearer every day the need for treatments of electron correlation that scale favorably with the number of electrons. Among them, the Kohn-Sham formulation of the Density Functional Theory (DFT) has become very popular thanks to its relatively low computational cost. However, present-day functionals have several problems due mainly to the so-called “correlation kinetic energy”, but most importantly, currently available functionals are not N-representable. (more…)

Since the beginning of this century, the spin-flip (SF) method has emerged as a very attractive alternative to the MC approach in the electronic structure study of molecular species with a multi-reference character wave function. The SF methodology is based on the construction of electronic wave functions through promotions of α electrons into empty β spin-orbitals in combination with the use of a high spin single determinant as the reference configuration. The SF idea has been implemented and applied with a variety of electronic structure formalisms: equation of motion coupled cluster (EOM-SF-CC), configuration interaction (SF-CI), and density functional theory (SF-DFT). (more…)


The rapid progress in electronic structure theory and computer technology during the last two decades has made possible the determination of accurate wave functions for small and medium size molecules. However, this is only the first step in solving problems of chemical interest as most application of quantum mechanics in chemistry deal with the computation of expectation values or density functions in terms of which the properties of sought are rationalized. This requirement is closely related with one of the major challenges of quantum chemistry: the development of practical procedures for the extraction of chemically interesting information from N-electron wavefunctions. (more…)

Finding the energies of bound states of screened Coulomb potentials has raised considerable interest for many years. There are many problems for which the reduction of the long-range Coulomb interactions due to the screening can drastically affect the results emerging from the consideration of bare Coulomb potentials. Thus, the calculation of thermodynamic properties of many-body systems in partially ionized gases, i.e., plasmas, has seen a rebirth since the inclusion of screening effects. The screened Coulomb potential can be represented by different models, the most famous of which is the analytic exponentially decaying potential of Yukawa type. (more…)

Hookean systems and Quantum DotsExact solutions of the Schrodinger equation for multiparticle systems with interparticle Coulombic interactions are unknown. One can try to find such exact solutions by modeling the interparticle interaction potential. Within this context, a much studied model is the Hookean two-electron atom, a system possessing a nucleus with charge +2 interacting through a harmonic potential with the electrons which, in turn, repel each other through the usual Coulomb interaction. (more…)

Contact person: Mario Piris. email: