Search results for "ETICA"
showing 10 items of 14083 documents
Data Reweighting in Metadynamics Simulations.
2020
The data collected along a metadynamics simulation can be used to recover information about the underlying unbiased system by means of a reweighting procedure. Here, we analyze the behavior of several reweighting techniques in terms of the quality of the reconstruction of the underlying unbiased free energy landscape in the early stages of the simulation and propose a simple reweighting scheme that we relate to the other techniques. We then show that the free energy landscape reconstructed from reweighted data can be more accurate than the negative bias potential depending on the reweighting technique, the stage of the simulation, and the adoption of well-tempered or standard metadynamics. …
Introducing Memory in Coarse-Grained Molecular Simulations
2021
[Image: see text] Preserving the correct dynamics at the coarse-grained (CG) level is a pressing problem in the development of systematic CG models in soft matter simulation. Starting from the seminal idea of simple time-scale mapping, there have been many efforts over the years toward establishing a meticulous connection between the CG and fine-grained (FG) dynamics based on fundamental statistical mechanics approaches. One of the most successful attempts in this context has been the development of CG models based on the Mori–Zwanzig (MZ) theory, where the resulting equation of motion has the form of a generalized Langevin equation (GLE) and closely preserves the underlying FG dynamics. In…
High excitations in coupled-cluster series: vibrational energy levels of ammonia
2004
The ammonia molecule containing large amplitude inversion motion is a revealing system in examining high-order correlation effects on potential energy surfaces. Correlation contributions to the equilibrium and saddle point geometries, inversion barrier height and vibrational energy levels, including inversion splittings, have been investigated. A six-dimensional Taylor-type series expansion of the Born–Oppenheimer potential energy surface, which is scaled to different levels of theory, is used to determine vibrational energy levels and inversion splittings variationally. The electronic energies are calculated by coupled-cluster methods, combining explicitly correlated R12 theory (which incl…
Dynamic Polarizability and Higher-Order Electric Properties of Fluorene, Carbazole, and Dibenzofuran
2019
Static electric properties, from the dipole moment to the second-hyperpolarizability tensor γ, of the 3-membered, isoelectronic ring molecules, fluorene (FL), carbazole (CR), and dibenzofuran (DBF), have been calculated at various levels of approximation. The electron correlation effects have been included at the coupled-cluster (CC) level, using CCSD and CC2 versions of the method. DFT calculations with the CAM-B3LYP functional have also been performed, and the results are compared to the CC values. The electric property-tailored Pol basis set and its more compact Z3Pol version have been employed in all static calculations. Differences between dipole polarizability values computed at the P…
Calculation of electronic g-tensors using coupled cluster theory.
2009
A scheme for the calculation of the electronic g-tensor at the coupled cluster (CC) level is presented. The reported implementation employs an effective one-electron spin-orbit operator, allows the inclusion of arbitrary excitations in the cluster operator, and offers various options concerning the treatment of orbital relaxation and choice of reference determinants. In addition, the use of gauge-including atomic orbitals (GIAOs) is possible to overcome the gauge origin problem. Benchmark calculations for the NH ((3)Sigma(-)) radical reveal the importance of electron correlation effects for the accurate prediction of the g-shift as well as the slow basis set convergence of such calculations…
Bond Dissociation Energies for Diatomic Molecules Containing 3d Transition Metals: Benchmark Scalar-Relativistic Coupled-Cluster Calculations for 20 …
2017
Benchmark scalar-relativistic coupled-cluster calculations for dissociation energies of the 20 diatomic molecules containing 3d transition metals in the 3dMLBE20 database ( J. Chem. Theory Comput. 2015 , 11 , 2036 ) are reported. Electron correlation and basis set effects are systematically studied. The agreement between theory and experiment is in general satisfactory. For a subset of 16 molecules, the standard deviation between computational and experimental values is 9 kJ/mol with the maximum deviation being 15 kJ/mol. The discrepancies between theory and experiment remain substantial (more than 20 kJ/mol) for VH, CrH, CoH, and FeH. To explore the source of the latter discrepancies, the …
Gas-Phase Synthesis of the Elusive Trisilicontetrahydride Species (Si3H4)
2016
The bimolecular gas-phase reaction of ground-state atomic silicon (Si; 3P) with disilane (Si2H6; 1A1g) was explored under single-collision conditions in a crossed molecular beam machine at a collision energy of 21 kJ mol–1. Combined with electronic structure calculations, the results suggest the formation of Si3H4 isomer(s) along with molecular hydrogen via indirect scattering dynamics through Si3H6 collision complex(es) and intersystem crossing from the triplet to the singlet surface. The nonadiabatic reaction dynamics can synthesize the energetically accessible singlet Si3H4 isomers in overall exoergic reaction(s) (−93 ± 21 kJ mol–1). All reasonable reaction products are either cyclic or …
Steering the excited state dynamics of a photoactive yellow protein chromophore analogue with external electric fields
2014
Abstract The first excited state of the Photoactive Yellow Protein chromophore exhibits a strong charge transfer character and the dipole moments of the excited and ground states differ significantly. Furthermore, the excited state charge distribution changes during the isomerization of this chromophore. These observations suggest that external electric fields can be used to control photo-isomerization, providing a new concept for developing photochromic devices, such as e-paper or optical memory. To test this idea, we performed excited state dynamics simulations and static calculations of a PYP chromophore analogue (pCK − ) in an external electric field. By adjusting direction and strength…
Enhanced alignment and orientation of polar molecules by vibrational resonant adiabatic passage
2007
The authors show that polar molecules can be adiabatically aligned and oriented by laser pulses more efficiently when the laser frequencies are vibrationally resonant. The aligned molecules are found in a superposition of vibrational pendular states, each associated with the alignment of the rotor in one vibrational state. The authors construct the dressed potential associated with this mechanism. Values of detunings and field amplitudes are given to optimize the degree of alignment and orientation for the CO molecule.
Carbonyl compounds of Tc, Re, and Bh: Electronic structure, bonding, and volatility.
2018
Calculations of molecular properties of M(CO)5 and MH(CO)5, where M = Tc, Re, and Bh, and of the products of their decomposition, M(CO)4 and MH(CO)4, were performed using density functional theory and coupled-cluster methods implemented in the relativistic program suits such as ADF, DIRAC, and ReSpect. The calculated first M—CO bond dissociation energies (FBDEs) of Bh(CO)5 and BhH(CO)5 turned out to be significantly weaker than those of the corresponding Re homologs. The reason for that is the relativistic destabilization and expansion of the 6d AOs, responsible for weaker σ-forth and π-back donations in the Bh compounds. The relativistic FBDEs of M(CO)5 have, therefore, a Λ-shape behavior …