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

Abstract

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.

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

“…Consequently, such differences, although small, tend to increase in systems in which the effectively unpaired electron density concentrates in atomic sites. 30,31 The results reported in Table II ͑partitioning of the physical space according to the fuzzy atom picture͒ show a similar trend, although the values E CC ͑in the C 2 H 6 , C 2 H 4 , and C 2 H 2 systems͒ turn out to be higher ͑in all the cases͒ than in the AIM picture. As in the previous table, the results derived from the one-center model are also closer to the SCF ones than those arising from the two-center model although the behavior of the differences ͉E AB SCF − E AB one-center ͉ is less clear.…”

Do Organometallic CH4–Me+p Adducts and X4H+ (X = P, As) Clusters Undergo Two-Electron Three-Center Interactions? Some Aspects of Discussion

“…7 The XX as well as X hb X sequences exhibit typical covalent interactions as described by the accumulation of the pairing density and the depletion of the unpaired one 7 and the values of the corresponding covalent bond orders (cf. Table 1).…”

“…6 In this respect, we have introduced a methodology to appropriately describe the different types of chemical interactions what we called a quantum version of the Lewis model. 7,8 This technique enabled us to go beyond the traditional chemical structures.…”

On the measure of electron correlation and entanglement in quantum chemistry based on the cumulant of the second-order reduced density matrix

“…These results are physically acceptable because ionic systems tend to transfer charge from one atom to another to preserve a closed-shell structure, while covalent bonds increase the charge density in the internuclear regions. 6,7 The second set is composed by the diatomic homonuclear molecules C 2 ,O 2 and the linear HBBH one in their triplet ground states, possessing all of them an inversion center; as can be observed all these systems show similar CCTM despite the number of electrons of the diatomic systems is different. These results are consistent with those observed in the first series because in these homonuclear molecules each atom possesses an even number of electrons providing a covalent bond and BH and BB bonds in HBBH are covalent.…”

“…2,3 Their influence on the electron distribution reveals through their relationships with the chemical descriptors and the topology of the distribution 4,5 and it is crucial in the understanding of the nature of the chemical bond. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] The fundamental chemical concepts are the summary of the physical information contained in the pth-order reduced density matrices ͑p-RDMs͒ of an N-electron molecular system ͑p Ͻ N͒ which are directly derived from the wave function. 2,3,10 Most of the attempts to describe the electron distribution in molecular systems have been concentrated on the spin blocks of the first-order reduced density matrices ͑spin up or ␣ and spin down or ␤ 1-RDMs͒, which determine electron and spin densities and provide intuitive interpretations of chemical data.…”