196,791 research outputs found
Description of high-spin restricted open-shell molecules with the Piris natural orbital functional
No full textThe Piris Natural Orbital Functional (PNOF) based on a new approach for the two-electron
cumulant is considered for the case of high-spin restricted open-shell systems. The theory is applied to the calculation of molecular energies, dipole moments, vertical ionization potentials (IP) and electron a¢ nities (EA) of 10 open-shell molecules. Vertical values of IP and EA have been used to evaluate the hardness. It has been observed that the results obtained using the PNOF method are comparable with the corresponding results obtained using CCSD(T) in case of energies and dipole moments. Best agreement between theory and experiment is achieved by PNOF for EA and hardness values. The calculated PNOF values for the mentioned properties are in good agreement with the available experimental data considering the basis sets used (6-31++G**)
Dispersion interactions within the Piris natural orbital functional theory: The helium dimer
No full textThe authors have investigated the description of the dispersion interaction within the Piris natural orbital functiona PNOF theory. The PNOF arises from an explicit antisymmetric approach for the two-particle cumulant in terms of two symmetric matrices, Delta and Pi. The functional forms of these matrices are obtained from the generalization of the two-particle system expressions, except for the off-diagonal elements of Delta. The mean value theorem and the partial sum rule obtained for the off-diagonal elements of Delta provide a prescription for deriving practical functionals. In particular, the previous employed approximation Jpp/2 for the mean values J*p affords several molecular properties but it is incapable to account for dispersion effects. In this work, the authors analyze a new approach for J*p obtained by factorization of the matrix Delta within the bounds on its off-diagonal elements imposed by the positivity conditions of the two-particle reduced density matrix. Additional terms for the matrix elements of ⌳ proportional to the square root of the holes are again introduced to describe properly the occupation numbers of the lowest occupied levels. The authors have found that the cross products between weakly occupied orbitals must be removed from the functional form of Pi to obtain a correct long-range asymptotic behavior. The PNOF is used to predict the binding energy as well as the equilibrium distance of the helium dimer. The results are compared with the full configuration-interaction calculations and the corresponding experimental data
DoNOF: An open-source implementation of natural-orbital-functional-based methods for quantum chemistry
No full textThe natural orbital functional theory (NOFT) has emerged as an alternative formalism to both density functional (DF) and wavefunction methods. In NOFT, the electronic structure is described in terms of the natural orbitals (NOs) and their occupation numbers (ONs). The approximate NOFs have proven to be more accurate than those of the density for systems with a significant multiconfigurational character, on one side, and scale better with the number of basis functions than correlated wavefunction methods, on the other side. A challenging task in NOFT is to efficiently perform orbital optimization. In this article we present DoNOF, our open source implementation based on diagonalizations that allows to obtain the resulting orbitals automatically orthogonal. The one-particle reduced-density matrix (1RDM) of the ensemble of pure-spin states provides the proper description of spin multiplets. The capabilities of the code are tested on the water molecule, namely, geometry optimization, natural and canonical representations of molecular orbitals, ionization potential, and electric moments. In DoNOF, the electron-pair-based NOFs developed in our group PNOF5, PNOF7 and PNOF7s are implemented. These JKL-only NOFs take into account most non-dynamic effects plus intrapair-dynamic electron correlation, but lack a significant part of interpair-dynamic correlation. Correlation corrections are estimated by the single-reference NOF-MP2 method that simultaneously calculates static and dynamic electron correlations taking as a reference the Slater determinant formed with the NOs of a previous PNOF calculation. The NOF-MP2 method is used to analyze the potential energy surface (PES) and the binding energy for the symmetric dissociation of the water molecule, and compare it with accurate wavefunction-based methods
Excited states by coupling Piris natural orbital functionals with extended random phase approximation
No full textIn this work, we extend the Piris natural orbital functionals (PNOFs) to
excited states by coupling their reconstructed second-order reduced density
matrices with the extended random-phase approximation (ERPA). We have named the
general implementation as PNOF-ERPA, and we refer to specific cases as
PNOF-ERPA0, PNOF-ERPA1 and PNOF-ERPA2, according to how the excitation operator
is built. The approaches have been tested in the first excited states of H2,
HeH+, LiH and Li2, showing good results compared with the full configuration
interaction (FCI) method. As expected, an increase in accuracy is observed when
going from ERPA0 to ERPA1 and ERPA2. We have also studied the effect of
electron correlation included by PNOF5, PNOF7 and the recently proposed global
NOF (GNOF) on the predicted excited states. PNOF5 appears to be good and may
even provide better results in very small systems, but including more electron
correlation becomes important as the system size increases, where PNOF7 and
GNOF provide better results. This effect can already be seen in the excitation
energies of the neon atom, where GNOF provides more accurate values than PNOF5
and PNOF7. Overall, the extension of PNOF to excited states has been
successful, making the PNOF-ERPA method promising for further applications.Comment: 18 pages, 10 figure
Correspondence re: Aguilera NS, Tomaszewski MM, Moad JC, Bauer FA, Taubenberger JK, Abbondanzo SL. Cutaneous follicle center lymphoma: A clinicopatho logic study of 19 cases. Mod Pathol. 2001;14 : 828-35. and Franco R, Fernandez-Vazquez A, Mollejo M, Cruz MA, Camacho FI, Garcia JF, Navarrete M, Piris MA. Cutaneous presentation of follicular lymphomas. Mod Pathol. 2001;14 : 913-9. In reply
No full textExcited States by Coupling Piris Natural Orbital Functionals with the Extended Random-Phase Approximation
No full textIn this work, we
explore the use of Piris natural orbital functionals
(PNOFs) to calculate excited-state energies by coupling their reconstructed
second-order reduced density matrix with the extended random-phase
approximation (ERPA). We have named the general method PNOF-ERPA,
and specific approaches are referred to as PNOF-ERPA0, PNOF-ERPA1,
and PNOF-ERPA2, according to the way the excitation operator is built.
The implementation has been tested in the first excited states of
H2, HeH+, LiH, Li2, and N2 showing good results compared to the configuration interaction (CI)
method. As expected, an increase in accuracy is observed on going
from ERPA0 to ERPA1 and ERPA2. We also studied the effect of electron
correlation included by PNOF5, PNOF7, and the recently proposed global
NOF (GNOF) on the predicted excited states. PNOF5 appears to be good
and may even provide better results in very small systems, but including
more electron correlation becomes important as the system size increases,
where GNOF achieves better results. Overall, the extension of PNOF
to excited states has been successful, making it a promising method
for further applications
Description of high‐spin restricted open‐shell molecules with the Piris natural orbital functional
No full textMarasmius tricystidiatus sp. nov. (Agaricales, Marasmiaceae) and its morphological and phylogenetic relationship with Marasmius jalapensis
No full textRamírez, Natalia A., Niveiro, Nicolás, Salvador-Montoya, Carlos A., Motta, Fátima Piris Da, Pérez, M. Laura, Popoff, Orlando F. (2021): Marasmius tricystidiatus sp. nov. (Agaricales, Marasmiaceae) and its morphological and phylogenetic relationship with Marasmius jalapensis. Phytotaxa 494 (1): 59-74, DOI: 10.11646/phytotaxa.494.1.3, URL: http://dx.doi.org/10.11646/phytotaxa.494.1.
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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