Dataset Information

Thermodynamic Properties of Crystalline Cellulose Allomorphs Studied with Dispersion-Corrected Density Functional Methods.

ABSTRACT: The phonon properties and thermodynamics of four crystalline cellulose allomorphs, Iα, Iβ, II, and III1, have been investigated using dispersion-corrected density functional theory (DFT). In line with experimental findings, the free energy differences between the studied cellulose allomorphs are small, less than 1 kJ/mol per atom. The calculated specific heat at constant volume (Cv) has been compared with the available experimental data in the temperature range 10-300 K. Quasiharmonic approximation has been employed to study thermodynamics and specific heat at constant pressure (Cp). For the studied temperature range of 10-400 K, the specific heat of all cellulose allomorphs shows very similar behavior. The calculated and experimental specific heat agree well at low temperatures below 100 K, but the deviation between theory and experiment increases with temperature. This may be due to increasing phonon anharmonicity as the temperature increases.

SUBMITTER: Srivastava D

PROVIDER: S-EPMC9570836 | biostudies-literature | 2022 Sep

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Thermodynamic Properties of Crystalline Cellulose Allomorphs Studied with Dispersion-Corrected Density Functional Methods.

Srivastava Divya D Ahopelto Jouni J Karttunen Antti J AJ

Molecules (Basel, Switzerland) 20220922 19

The phonon properties and thermodynamics of four crystalline cellulose allomorphs, Iα, Iβ, II, and III1, have been investigated using dispersion-corrected density functional theory (DFT). In line with experimental findings, the free energy differences between the studied cellulose allomorphs are small, less than 1 kJ/mol per atom. The calculated specific heat at constant volume (Cv) has been compared with the available experimental data in the temperature range 10-300 K. Quasiharmonic approximat ...[more]

PMID: 36234777

Similar Datasets

Project description:Imidazo[1,2-a]pyrazines are cyclic amidine-type compounds composed of α-amino acid residues. A full structural identification of these molecules constitutes an analytical challenge, especially when imidazo[1,2-a]pyrazines are obtained from physical processes (e.g., sublimation and pyrolysis of amino acids). A valuable source of molecular information can be obtained from absorption spectroscopies and related techniques encompassing the use of metallic substrates. The aim of this study is to provide new knowledge and insights into the noncovalent intermolecular interactions between imidazo[1,2-a]pyrazines and two Ag n (n = 4 and 20) clusters using density functional theory (DFT) methods. Semiempirical DFT dispersion (DFT-D) corrections were addressed using Grimme's dispersion (GD2) and Austin-Petersson-Frisch (APF) functionals in conjunction with the 6-31+G(d,p) + LANL2DZ mixed basis set. These DFT-D methods describe strong interactions; besides, in all cases, the APF dispersion (APF-D) energies of interaction appear to be consistently overestimated. In comparison with B3LYP calculations, the mean values for the difference in the energies of interaction calculated are 2.25 (GD2) and 6.24 (APF-D) kcal mol-1 for Ag4-molecules, and 2.30 (GD2) and 8.53 (APF-D) kcal mol-1 for Ag20-molecules. The effect of applying GD2 and APF-D corrections to the noncovalent complexes is nuanced in the intermolecular distances calculated, mainly in the Ag···N(amidine) bonding, which appears to play the most important role for the adsorptive process. Selective enhancement and considerable red shifts for Raman vibrations suggest strong interactions, whereas a charge redistribution involving the metallic substrate and the absorbate leads to a significant rearrangement of frontier molecular orbitals mainly in the Ag20-molecule complexes. Finally, time-dependent DFT calculations were carried out to access the orbital contributions to each of the transitions observed in the absorption spectrum. The corresponding UV-vis spectra involve transitions in the visible region at around 400 and 550 nm for the Ag4-molecule and the Ag20-molecule complexes, respectively.

Project description:Time-dependent density functional theory has become state-of-the-art for describing photophysical and photochemical processes in extended materials because of its affordable cost. The inclusion of exact exchange was shown to be essential for the correct description of the long-range asymptotics of electronic interactions and thus a well-balanced description of valence, Rydberg, and charge-transfer excitations. Several approaches for an efficient treatment of exact exchange have been established for the ground state, while implementations for excited-state properties are rare. Furthermore, the high computational costs required for excited-state properties in comparison to ground-state computations often hinder large-scale applications on periodic systems with hybrid functional accuracy. We therefore propose two approximate schemes for improving computational efficiency for the treatment of exact exchange. Within the auxiliary density matrix method (ADMM), exact exchange is estimated using a relatively small auxiliary basis and the introduced basis set incompleteness error is compensated by an exchange density functional correction term. Benchmark results for a test set of 35 molecules demonstrate that the mean absolute error introduced by ADMM is smaller than 0.3 pm for excited-state bond lengths and in the range of 0.02-0.04 eV for vertical excitation, adiabatic excitation, and fluorescence energies. Computational timings for a series of covalent-organic frameworks demonstrate that a speed-up of at least 1 order of magnitude can be achieved for excited-state geometry optimizations in comparison to conventional hybrid functionals. The second method is to use a semiempirical tight binding approximation for both Coulomb and exchange contributions to the excited-state kernel. This simplified Tamm-Dancoff approximation (sTDA) achieves an accuracy comparable to approximated hybrid density functional theory when referring to highly accurate coupled-cluster reference data. We find that excited-state bond lengths deviate by 1.1 pm on average and mean absolute errors in vertical excitation, adiabatic excitation, and fluorescence energies are in the range of 0.2-0.5 eV. In comparison to ADMM-approximated hybrid functional theory, sTDA accelerates the computation of broad-band excitation spectra by 1 order of magnitude, suggesting its potential use for large-scale screening purposes.

Dataset Information

Thermodynamic Properties of Crystalline Cellulose Allomorphs Studied with Dispersion-Corrected Density Functional Methods.

Publications

Thermodynamic Properties of Crystalline Cellulose Allomorphs Studied with Dispersion-Corrected Density Functional Methods.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets