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11 pages, 2477 KiB

Open AccessArticle

DFT Study of Si/Al Ratio and Confinement Effects on the Energetics and Vibrational Properties of some Aza-Aromatic Molecules Adsorbed on H-ZSM-5 Zeolite

by Martine Castellà-Ventura, Alain Moissette and Emile Kassab

Computation 2020, 8(3), 81; https://0-doi-org.brum.beds.ac.uk/10.3390/computation8030081 - 10 Sep 2020

Cited by 1 | Viewed by 2497

Abstract

The Si/Al ratio and confinement effects of zeolite framework on energetics and vibrational frequencies of pyridine and 4,4′-bipyridine adsorbed on Brønsted acid sites in the straight channel of H-ZSM-5 are investigated by DFT calculations at the B3LYP and M06-2X+D3 levels. The straight channel [...] Read more.

The Si/Al ratio and confinement effects of zeolite framework on energetics and vibrational frequencies of pyridine and 4,4′-bipyridine adsorbed on Brønsted acid sites in the straight channel of H-ZSM-5 are investigated by DFT calculations at the B3LYP and M06-2X+D3 levels. The straight channel of H-ZSM-5 is simulated by a cluster of 32 tetrahedral centers covering the intersection between straight and zigzag channels. Pyridine and 4,4′-bipyridine adsorption at two different sites in the intersection (open region) and/or in the narrow region situated between two intersections (closed region) is studied. For two Si/Al ratios (31, 15), the ion pair complexes formed by proton transfer upon pyridine and 4,4′-bipyridine adsorption in the open region and for the first time in the closed region are characterized. Our results indicate: (i) the stability for all adsorption complexes is essentially governed by the dispersive van der Waals interactions and the open region is energetically more favorable than the closed region owing to the predominance of the dispersive interactions over the steric constraints exerted by the confinement effects; (ii) as the Al centers are sufficiently spaced apart, Si/Al ratio does not influence pyridine adsorption energy, but significantly affects the adsorption energies and the relative stability of 4,4′-bipyridine complexes; (iii) neither Si/Al ratio nor confinement significantly influence pyridine and 4,4′-bipyridine vibrational frequencies within their complexes. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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13 pages, 2678 KiB

Open AccessArticle

The Low Lying Double-Exciton State of Conjugated Diradicals: Assessment of TDUDFT and Spin-Flip TDDFT Predictions

by Sofia Canola, Yasi Dai and Fabrizia Negri

Computation 2019, 7(4), 68; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040068 - 26 Nov 2019

Cited by 9 | Viewed by 3681

Abstract

Conjugated singlet ground state diradicals have received remarkable attention owing to their potential applications in optoelectronic devices. A distinctive character of these systems is the location of the double-exciton state, a low lying excited state dominated by the doubly excited HOMO,HOMOLUMO,LUMO configuration, (where [...] Read more.

Conjugated singlet ground state diradicals have received remarkable attention owing to their potential applications in optoelectronic devices. A distinctive character of these systems is the location of the double-exciton state, a low lying excited state dominated by the doubly excited HOMO,HOMOLUMO,LUMO configuration, (where HOMO=highest occupied molecular orbital, LUMO=lowest unoccupied molecular orbital) which may influence optical and other photophysical properties. In this contribution we investigate this specific excited state, for a series of recently synthesized conjugated diradicals, employing time dependent density functional theory (TDDFT) based on the unrestricted parallel spin reference configuration in the spin-flip formulation (SF-TDDFT) and standard TD calculations based on the unrestricted antiparallel spin reference configuration (TDUDFT). The quality of computed results is assessed considering diradical and multiradical descriptors, and the excited state wavefunction composition. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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16 pages, 838 KiB

Open AccessArticle

The Role of the Reduced Laplacian Renormalization in the Kinetic Energy Functional Development

by Szymon Śmiga, Lucian A. Constantin, Fabio Della Sala and Eduardo Fabiano

Computation 2019, 7(4), 65; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040065 - 12 Nov 2019

Cited by 13 | Viewed by 2714

Abstract

The Laplacian of the electronic density diverges at the nuclear cusp, which complicates the development of Laplacian-level meta-GGA (LLMGGA) kinetic energy functionals for all-electron calculations. Here, we investigate some Laplacian renormalization methods, which avoid this divergence. We developed two different LLMGGA functionals, which [...] Read more.

The Laplacian of the electronic density diverges at the nuclear cusp, which complicates the development of Laplacian-level meta-GGA (LLMGGA) kinetic energy functionals for all-electron calculations. Here, we investigate some Laplacian renormalization methods, which avoid this divergence. We developed two different LLMGGA functionals, which improve the kinetic energy or the kinetic potential. We test these KE functionals in the context of Frozen-Density-Embedding (FDE), for a large palette of non-covalently interacting molecular systems. These functionals improve over the present state-of-the-art LLMGGA functionals for the FDE calculations. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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14 pages, 516 KiB

Open AccessArticle

Efficient Evaluation of Molecular Electrostatic Potential in Large Systems

by Rafael Lopez, Frank Martinez, Ignacio Ema, Jose Manuel Garcia de la Vega and Guillermo Ramirez

Computation 2019, 7(4), 64; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040064 - 12 Nov 2019

Cited by 4 | Viewed by 2682

Abstract

An algorithm for the efficient computation of molecular electrostatic potential is reported. It is based on the partition/expansion of density into (pseudo) atomic fragments with the method of Deformed Atoms in Molecules, which allows to compute the potential as a sum of atomic [...] Read more.

An algorithm for the efficient computation of molecular electrostatic potential is reported. It is based on the partition/expansion of density into (pseudo) atomic fragments with the method of Deformed Atoms in Molecules, which allows to compute the potential as a sum of atomic contributions. These contributions are expressed as a series of irregular spherical harmonics times effective multipole moments and inverse multipole moments, including short-range terms. The problem is split into two steps. The first one consists of the partition/expansion of density accompanied by the computation of multipole moments, and its cost depends on the size of the basis set used in the computation of electron density within the Linear Combination of Atomic Orbitals framework. The second one is the actual computation of the electrostatic potential from the quantities calculated in the first step, and its cost depends on the number of computation points. For a precision in the electrostatic potential of six decimal figures, the algorithm leads to a dramatic reduction of the computation time with respect to the calculation from electron density matrix and integrals involving basis set functions. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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6 pages, 200 KiB

Open AccessArticle

Coordinate Scaling in Time-Independent Excited-State Density Functional Theory for Coulomb Systems

by Ágnes Nagy

Computation 2019, 7(4), 59; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040059 - 13 Oct 2019

Cited by 1 | Viewed by 2093

Abstract

A time-independent density functional theory for excited states of Coulomb systems has recently been proposed in a series of papers. It has been revealed that the Coulomb density determines not only its Hamiltonian, but the degree of excitation as well. A universal functional [...] Read more.

A time-independent density functional theory for excited states of Coulomb systems has recently been proposed in a series of papers. It has been revealed that the Coulomb density determines not only its Hamiltonian, but the degree of excitation as well. A universal functional valid for any excited state has been constructed. The excited-state Kohn–Sham equations bear resemblance to those of the ground-state theory. In this paper, it is studied how the excited-state functionals behave under coordinate scaling. A few relations for the scaled exchange, correlation, exchange-correlation, and kinetic functionals are presented. These relations are expected to be advantageous for designing approximate functionals. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

14 pages, 4613 KiB

Open AccessArticle

First-Principles Calculations of Structural, Mechanical, and Electronic Properties of the B2-Phase NiTi Shape-Memory Alloy Under High Pressure

by Fang Yu and Yu Liu

Computation 2019, 7(4), 57; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040057 - 30 Sep 2019

Cited by 11 | Viewed by 4084

Abstract

A first-principles calculation program is used for investigating the structural, mechanical, and electronic properties of the cubic NiTi shape-memory alloy (SMA) with the B2 phase under high pressure. Physical parameters including dimensionless ratio, elastic constants, Young’s modulus, bulk modulus, shear modulus, ductile-brittle transition, [...] Read more.

A first-principles calculation program is used for investigating the structural, mechanical, and electronic properties of the cubic NiTi shape-memory alloy (SMA) with the B2 phase under high pressure. Physical parameters including dimensionless ratio, elastic constants, Young’s modulus, bulk modulus, shear modulus, ductile-brittle transition, elastic anisotropy, and Poisson’s ratio are computed under different pressures. Results indicate that high pressure enhances the ability to resist volume deformation along with the ductility and metallic bonds, but the biggest resistances to elastic and shear deformation occur at

P = 35 GPa

for the B2-phase NiTi SMA. Meanwhile, the strong anisotropy produced by the high pressure will motivate the cross-slip process of screw dislocations, thereby improving the plasticity of the B2-phase NiTi SMA. Additionally, the results of the density of states (DOS) reveal that the B2-phase NiTi SMA is essentially characterized by the metallicity, and it is hard to induce the structural phase transition for the B2-phase NiTi SMA under high pressure, which provides valuable guidance for designing and applying the NiTi SMA under high pressure. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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13 pages, 1126 KiB

Open AccessArticle

Chemical-Reactivity Properties, Drug Likeness, and Bioactivity Scores of Seragamides A–F Anticancer Marine Peptides: Conceptual Density Functional Theory Viewpoint

by Norma Flores-Holguín, Juan Frau and Daniel Glossman-Mitnik

Computation 2019, 7(3), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7030052 - 14 Sep 2019

Cited by 25 | Viewed by 3650

Abstract

A methodology based on concepts that arose from Density Functional Theory (CDFT) was chosen for the calculation of global and local reactivity descriptors of the Seragamide family of marine anticancer peptides. Determination of active sites for the molecules was achieved by resorting to [...] Read more.

A methodology based on concepts that arose from Density Functional Theory (CDFT) was chosen for the calculation of global and local reactivity descriptors of the Seragamide family of marine anticancer peptides. Determination of active sites for the molecules was achieved by resorting to some descriptors within Molecular Electron Density Theory (MEDT) such as Fukui functions. The pKas of the six studied peptides were established using a proposed relationship between this property and calculated chemical hardness. The drug likenesses and bioactivity properties of the peptides considered in this study were obtained by resorting to a homology model by comparison with the bioactivity of related molecules in their interaction with different receptors. With the object of analyzing the concept of drug repurposing, a study of potential AGE-inhibition abilities of Seragamides peptides was pursued by comparison with well-known drugs that are already available as pharmaceuticals. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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Review

Jump to: Research

8 pages, 576 KiB

Open AccessReview

Emerging DFT Methods and Their Importance for Challenging Molecular Systems with Orbital Degeneracy

by Emilio San-Fabián Maroto and Juan-Carlos Sancho-García

Computation 2019, 7(4), 62; https://0-doi-org.brum.beds.ac.uk/10.3390/computation7040062 - 03 Nov 2019

Cited by 5 | Viewed by 3460

Abstract

We briefly present some of the most modern and outstanding non-conventional density-functional theory (DFT) methods, which have largely broadened the field of applications with respect to more traditional calculations. The results of these ongoing efforts reveal that a DFT-inspired solution always exists even [...] Read more.

We briefly present some of the most modern and outstanding non-conventional density-functional theory (DFT) methods, which have largely broadened the field of applications with respect to more traditional calculations. The results of these ongoing efforts reveal that a DFT-inspired solution always exists even for pathological cases. Among the set of emerging methods, we specifically mention FT-DFT, OO-DFT, RSX-DFT, MC-PDFT, and FLOSIC-DFT, complementing the last generation of existing density functionals, such as local hybrid and double-hybrid expressions. Full article

(This article belongs to the Special Issue New Advances in Density Functional Theory and Its Application)

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