Distribution of odd electrons in ground-state molecules

et al. 2007

Articles you may be interested inA new ab initio potential energy surface for the collisional excitation of HCN by para-and ortho-H2 J. Chem. Phys. 139, 224301 (2013) This article is a continuation of our previous paper on schemes of energy decompositions of molecular systems in the real space ͓D. R. Alcoba et al., J. Chem. Phys. 122, 074102 ͑2005͔͒ now using correlated state functions. We study, according to physical arguments, the appropriate management of the density cumulant arising from the second-order reduced density matrix at correlated level, whose contributions can be assigned to one-center or to two-center terms in the energy partitioning. Our treatments are applied within two physical space partitioning schemes: the Bader partitioning into atomic basins and the fuzzy atom procedure. The results obtained in selected molecules are analyzed and discussed in detail.

Section: Computational Aspects and Resultssupporting

confidence: 55%

Energy decompositions according to physical space partitioning schemes: Treatments of the density cumulant

Alcoba

Torre

et al. 2007

“…The u matrix is the appropriate tool to describe the effectively unpaired electron density which is related to the spin density and to the nonuniformity of the electron cloud in the molecular or natural orbital populations. [5][6][7][8] In the case of a double occupation numbers such as the closed-shell Hartree Fock or the density-functional theory ͑DFT͒, in which ͑u͒ ͑r͒ is intrinsically zero, are fulfilled,…”

Section: B the Topological Studymentioning

confidence: 99%

“…This algorithm allows one to perform a decomposition of the electron density into two parts, the paired density matrix and the effectively unpaired density matrix. [5][6][7][8][9] This result provides the appropriate method for studying the topology of each component in an independent way and consequently to draw out all the features of the electron density. The main goal of this work is to perform the a͒ partitioning of the electron density within the pth-RDM framework into two terms so that the properties of both of them can topologically be analyzed.…”

Section: Introductionmentioning

confidence: 99%

Electron-density topology in molecular systems: Paired and unpaired densities

Lobayan

Bochicchio

et al. 2005

101

Articles you may be interested inThis work studies the partitioning of the electron density into two contributions which are interpreted as the paired and the effectively unpaired electron densities. The topological features of each density field as well as of the total density are described localizing the corresponding critical points in simple selected molecules ͑local formalism͒. The results show that unpaired electron-density concentrations occur out of the topological bonding regions whereas the paired electron densities present accumulations inside those regions. A comparison of these results with those arising from population analysis techniques ͑nonlocal or integrated formalisms͒ is reported.

“…[18][19][20][21][22][23][24] In those references, it has also been suggested that the numerical value of the i ( 1 D i i − 2 2 D ii ii ) quantity could constitute an alternative measure of the number of effectively unpaired electrons corresponding to the wave function (N, S) and this result could be compared with those reported using other methods. [25][26][27][28][29][30][31][32][33] According to Eq. (3), the number of unpaired electrons can also be evaluated in terms of the expectation value of the seniority operator.…”

Section: A the Seniority Number For A Spin-adapted Wave Functionmentioning

confidence: 99%

Seniority number in spin-adapted spaces and compactness of configuration interaction wave functions

Alcoba

Torre

et al. 2013

This work extends the concept of seniority number, which has been widely used for classifying N-electron Slater determinants, to wave functions of N electrons and spin S, as well as to N-electron spin-adapted Hilbert spaces. We propose a spin-free formulation of the seniority number operator and perform a study on the behavior of the expectation values of this operator under transformations of the molecular basis sets. This study leads to propose a quantitative evaluation for the convergence of the expansions of the wave functions in terms of Slater determinants. The non-invariant character of the seniority number operator expectation value of a wave function with respect to a unitary transformation of the molecular orbital basis set, allows us to search for a change of basis which minimizes that expectation value. The results found in the description of wave functions of selected atoms and molecules show that the expansions expressed in these bases exhibit a more rapid convergence than those formulated in the canonical molecular orbital bases and even in the natural orbital ones.