Liquid actuated gravity experiments

We describe a new actuation technique for gravity experiments based on a liquid field mass. The Characterizing idea is to modulate the gravity force acting on a test mass by controlling the level of a liquid in a suitable container. This allows to obtain a periodical gravity force without moving parts (except the liquid level) close to the TM. We describe in detail the most relevant aspects of the liquid actuator and discuss how it can be used in gravity experiments. In particular we analyse an application to test the inverse square law in the mm to cm distance region

Measurement of gravitational and thermal effects in a liquid-actuated torsion pendulum

We describe a proof-of-principle experiment aiming to investigate the inverse-square law of gravitation at the centimeter scale. The sensor is a two-stage torsion pendulum, while actuation is accomplished by a variable liquid mass. The time-varying gravitational force is related to the level of the circulating fluid in one or two containers at a short distance from the test mass, with all moving mechanical parts positioned at a large distance. We provide a description of the apparatus and present the first results. We identified a systematic effect of thermal origin, producing offsets of few fNm in torque and of about 10 pN in force. When this effect is neutralized, the measurements agree well with the predictions of simulations. We also discuss the upcoming instrument upgradations and the expected sensitivity improvement that will allow us to perform measurements with adequate accuracy to investigate the unexplored regions of the α−λ parameter space of a Yukawa-like deviation from the Newtonian potential

N-Heterocyclic carbene copper(I) catalysed N-methylation of amines using CO2

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), the EPSRC (DTG011 EP/J500549/1) and the King Abdullah University of Science and Technology for funding, and the EPSRC National Mass Spectrometry Service Centre at Swansea University for HMRS analyses.The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.Publisher PDFPeer reviewe

Accurate Gas Phase Formation Enthalpies of Alloys and Refractories Decomposition Products

Accurate gas phase formation enthalpies, Î\u94Hf, of metal oxides and halides are critical for the prediction of the stability of high temperature materials used in the aerospace and nuclear industries. Unfortunately, the experimental Î\u94Hfvalues of these compounds in the most used databases, such as the NIST-JANAF database, are often reported with large inaccuracy, while some other Î\u94Hfvalues clearly differ from the value predicted by CCSD(T) methods. To address this point, in this work we systematically predicted the Î\u94Hfvalues of a series of these compounds having a group 4, 6, or 14 metal. The Î\u94Hfvalues in question were derived within a composite Feller-Dixon-Peterson (FDP) scheme based protocol that combines the DLPNO-CCSD(T) enthalpy of ad hoc designed reactions and the experimental Î\u94Hfvalues of few reference complexes. In agreement with other theoretical studies, we predict the Î\u94Hfvalues for TiOCl2, TiOF2, GeF2, and SnF4to be significantly different from the values tabulated in NIST-JANAF and other sources, which suggests that the tabulated experimental values are inaccurate. Similarly, the predicted Î\u94Hfvalues for HfCl2, HfBr2, HfI2, MoOF4, MoCl6, WOF4, WOCl4, GeO2, SnO2, PbBr4, PbI4, and PbO2also clearly differ from the tabulated experimental values, again suggesting large inaccuracy in the experimental values. In the case when largely different experimental values are available, we point to the value that is in better agreement with our results. We expect the Î\u94Hfvalues reported in this work to be quite accurate, and thus, they might be used in thermodynamic calculations, because the effects from core correlation, relativistic effects, and basis set incompleteness were included in the DLPNO-CCSD(T) calculations. T1 and T2 values were thoroughly monitored as indicators of the quality of the reference Hartree-Fock orbitals (T1) and potential multireference character of the systems (T2)

Heats of Formation of Medium-Sized Organic Compounds from Contemporary Electronic Structure Methods

Computational electronic structure calculations are routinely undertaken to predict thermodynamic properties of various species. However, the application of highly accurate wave function theory methods, such as the "gold standard" coupled cluster approach including single, double, and partly triple excitations in perturbative fashion, CCSD(T), to large molecules is limited due to high computational cost. In this work, the promising domain based local pair natural orbital coupled cluster approach, DLPNO-CCSD(T), has been tested to reproduce 113 accurate formation enthalpies of medium-sized molecules (few dozens heavy atoms) important for bio- and combustion chemistry via the reaction based Feller-Peterson-Dixon approach. For comparison, eight density functional theory (B3LYP, B3LYP-D3, PBE0, PBE0-D3, M06, M06-2X, Ï\u89B97X-D3, and Ï\u89B97M-V) and MP2-based (B2PLYP-D3, PWPB95-D3, B2T-PLYP, B2T-PLYP-D, B2GP-PLYP, DSD-PBEP86-D3, SCS-MP2, and OO-SCS-MP2) methods have been tested. The worst performance has been obtained for the standard hybrid DFT functionals, PBE0 (mean unsigned error (MUE)/mean signed error (MSE) = 9.1/6.0 kcal/mol) and B3LYP (MUE/MSE = 13.5/-13.3 kcal/mol). The influence of an empirical dispersion correction term on these functionals' performance is not homogeneous: B3LYP performance is improved (B3LYP-D3 (MUE/MSE = 6.0/0.8 kcal/mol)); meanwhile PBE0 performance is worse (PBE0-D3 (MUE/MSE = 14.1/13.6 kcal/mol)). The Minnesota functionals, M06 (MUE/MSE = 3.8/-2.0 kcal/mol) and M06-2X (MUE/MSE = 3.5/3.0 kcal/mol), and recently developed Ï\u89B97X-D3 (MUE/MSE = 3.2/0.2 kcal/mol) and Ï\u89B97M-V (MUE/MSE = 2.2/1.3 kcal/mol) methods provided significantly better formation enthalpies. Enthalpies of similar quality can also be obtained from some double hybrid methods (B2PLYP-D3 (MUE/MSE = 4.7/2.0 kcal/mol), PWPB95-D3 (MUE/MSE = 4.3/3.2 kcal/mol), B2T-PLYP (MUE/MSE = 4.1/-3.0 kcal/mol), and B2T-PLYP-D (MUE/MSE = 3.3/1.7 kcal/mol)). The two spin component scaled (SCS) MP2 methods resulted in even smaller errors (SCS-MP2 (MUE/MSE = 1.9/1.2 kcal/mol) and OO-SCS-MP2 (MUE/MSE = 1.6/0.1 kcal/mol)). The best performance was found for the frozen core (FC) DLPNO-CCSD(T) method with a MUE/MSE of 1.6/-1.2 kcal/mol. The performance of the DLPNO-CCSD(T) method can be further improved by running the post-SCF calculations on the B3LYP orbitals: the MUE/MSE for the DLPNO-CCSD(T,B3LYP) approximation is 1.2/-0.4 kcal/mol. We recommend the DLPNO-CCSD(T,B3LYP) method for black box applications in thermodynamics of medium-sized organic molecules when the canonical CCSD(T) calculations with basis sets of reasonable quality are prohibitively expensive

Application of Semiempirical Methods to Transition Metal Complexes: Fast Results but Hard-to-Predict Accuracy

A series of semiempirical PM6* and PM7 methods has been tested in reproducing relative conformational energies of 27 realistic-size complexes of 16 different transition metals (TMs). An analysis of relative energies derived from single-point energy evaluations on density functional theory (DFT) optimized conformers revealed pronounced deviations between semiempirical and DFT methods, indicating a fundamental difference in potential energy surfaces (PES). To identify the origin of the deviation, we compared fully optimized PM7 and respective DFT conformers. For many complexes, differences in PM7 and DFT conformational energies have been confirmed often manifesting themselves in false coordination of some atoms (H, O) to TMs and chemical transformations/distortion of coordination center geometry in PM7 structures. Despite geometry optimization with fixed coordination center geometry leading to some improvements in conformational energies, the resulting accuracy is still too low to recommend explored semiempirical methods for out-of-the-box conformational search/sampling: careful testing is always needed