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Materials and RCC quality requirements
Published in L. Berga, J.M. Buil, C. Jofré, S. Chonggang, Roller Compacted Concrete Dams, 2018
The use of additives in RCC is a relatively new approach. The use of chemical additives has increased since mid 90’s, aiming at controlling the “Set” and broadening the operational margin for RCC transportation and compaction[13&14]. Its use has propitiated, besides control of the set, gains in resistant properties and that becomes a technical parameter with economic implications that must be analyzed. The choice of any admixture should be confirmed by laboratory trial mixes and ideally after full-scale trials. Particular admixtures work well with particular cementitious materials and not so well with other materials.
A case study of density functional theory and domain-based local pair natural orbital coupled cluster for vibrational effects on EPR hyperfine coupling constants: vibrational perturbation theory versus ab initio molecular dynamics
Published in Molecular Physics, 2020
Alexander A. Auer, Van Anh Tran, Bikramjit Sharma, Georgi L. Stoychev, Dominik Marx, Frank Neese
Due to the self interaction error in the GGA approach to DFT, widely used functionals in AIMD simulations such as PBE [69,70] or BLYP [71,72] are not good candidates for open-shell systems. Standard hybrid functionals, fortunately, are known to perform much more reliably in such cases since a proper admixture of nonlocal HF exchange on top of the semilocal GGA exchange approximately counteracts spin delocalisation artefacts. Specifically the PBE0 functional in conjunction with a suitable basis set ‘ provides remarkably accurate magnetic properties at reasonable computational costs ’ [73] in vacuum (together with yielding the corresponding molecular equilibrium structures) as well as in aqueous solution [74]. Next, it has been found out that the revPBE0-D3 functional provides a very accurate description of the full-dimensional many-body potential energy surface for AIMD simulations of liquid bulk water as confirmed by adding nuclear quantum effects and comparing thereafter important observables to experimental data that quantify the structural, dynamical, and vibrational properties of water at ambient conditions [75].
Density functionals for nondynamical correlation constructed from an upper bound to the exact exchange energy density
Published in Molecular Physics, 2019
Benjamin G. Janesko, Giovanni Scalmani, Michael J. Frisch
Tables 4 and 5 show that constant admixture of Equation (13) indeed provides ‘global-hybrid-like’ corrections to thermochemistry and kinetics. Adding a constant fraction of Equation (13) to HF exchange gives LHup-HF thermochemistry RMSD significantly improved on HF-PBE, with little change in reaction barriers. (Test post-PBE0 calculations give nearly identical LHup-HF MGAE ME,MAE,RMSD of 1.6,15.5,19.6 kcal/mol.) Subtracting a constant fraction of Equation (13) from PBE gives LHup-PBE thermochemistry RMSD significantly improved over PBE, with little change in reaction barriers. (To emphasise that this is not a fluke or an artefact, note from Table 2 that Equation (13) reduces the density-driven errors [102] partly responsible for GGAs' inaccurate radical reaction barriers [81,103].) Adding a constant fraction of Equation (13) to a PBE45 global hybrid including 45% HF exchange modestly improves thermochemistry and degrades reaction barriers, giving overall performance comparable to other PBE global hybrids consistent with Figure 7.