Adequate Basis Set Research Articles

Study of the structural and optoelectronic properties of dye solar cells based on phosphonic acid anchoring by DFT functionals

The choice of the functional and an adequate basis set for reproducing the experimental data of T4-BTDA phosphonic acid-based dye is made by using six functionals and four atomic basis sets.

Calculation of spin-orbit couplings using RASCI spinless one-particle density matrices: Theory and applications.

This work presents the formalism and implementation for calculations of spin-orbit couplings (SOCs) using the Breit-Pauli Hamiltonian and non-relativistic wave functions described by the restricted active space configuration interaction (RASCI) method with general excitation operators of spin-conserving spin-flipping, ionizing, and electron-attaching types. The implementation is based on the application of the Wigner-Eckart theorem within the spin space, which enables the calculation of the entire SOC matrix based on the explicit calculation of just one transition between the two spin multiplets. Numeric results for a diverse set of atoms and molecules highlight the importance of a balanced treatment of correlation and adequate basis sets and illustrate the overall robust performance of RASCI SOCs. The new implementation is a useful addition to the methodological toolkit for studying spin-forbidden processes and molecular magnetism.

Exploring the spectroscopic constants of 2 Π u , 2 Σ u + (main and a satellite) and 2 Π g states of N 2 + ion using the Fock-space coupled-cluster with eigenvalue independent partitioning

The Fock-space coupled-cluster (FSCC) method appears as a robust computational scheme if reformulated within the eigenvalue independent partitioning framework (EIP-FSCC) which efficiently deals with the intruder states that cause convergence problems in its standard effective Hamiltonian format. Within such a reformulation not only the so-called main (principal) root of the effective Hamiltonian version are attainable, but also the alternative satellite roots appear from the higher-sectors of the corresponding matrix (that is properly constructed) upon its direct diagonalization. Selective spectroscopic constants of 2 Π u , 2 Σ u + (main and satellite), and 2 Π g states of N 2 + ion have here been estimated using the EIP-FSCC by exploiting various truncation schemes of cluster operators (EIP-FSCCSD and EIP-FSCCSDτ). EIP-FSCCSDτ includes the set of full connected triple excitation operators for the ionized states where as perturbative is considered by CCSDT1-a approximation. This work indicates that the EIP-FSCCSDτ, compared to EIP-FSCCSD scheme, is capable of providing nice agreement with experiment provided an adequate basis set is used.

Electron Density Topological Analysis of Adsorbates on Pt and Pt Alloy Fuel Cell Catalytic Layers

Phenomenological models based on adsorbate orbital occupation have shortcomings. Orbital charges, obtained by integration of densities-of-states (DOS) spectra, do not always correlate to bond strengths. Bader and co-workers have developed the quantum theory of atoms in molecules (QTAIM), which is based on the topology of electron densities, gradients and Laplacians of those densities to describe atoms and bonds of chemical systems. The advantage of QTAIM analyses is that they are basis set and method independent, as long as a minimally adequate basis set is used. We apply both QTAIM and adsorbate orbital approaches to the study of co-adsorption of water and carbon monoxide on Pt and Pt alloy catalytic surfaces relevant to polymer electrolyte fuel cell anodes, and show how the use of both approaches are complementary.

Theoretical study of the complexes of dichlorobenzene isomers with argon. II. SAPT analysis of the intermolecular interaction

The interaction of argon with dichlorobenzene isomers (DCB-Ar) has been analyzed with the help of the symmetry-adapted perturbation theory based on the density functional description of monomer properties (DFT-SAPT). The global potential energy surface (PES) of these complexes determined from the DFT-SAPT interaction energy (Eint) values has been compared to the CCSD(T) (coupled cluster method including single and double excitations with perturbative triple excitations) PES reported in the companion Paper I [J. Makarewicz and L. Shirkov, J. Chem. Phys. 150, 074301 (2019)]. The equilibrium structures and the binding energies found using DFT-SAPT and CCSD(T) methods combined with adequate basis sets are in good agreement. Besides DCB-Ar, we confirmed that DFT-SAPT gives accurate values of these quantities for other complexes containing an aromatic molecule and Ar. However, DFT-SAPT PES of DCB-Ar is flatter than the corresponding CCSD(T) one. As a result, the intermolecular vibrational energies are systematically underestimated. The analytical form of the important interrelations between SAPT components of Eint, established previously by us [J. Makarewicz and L. Shirkov, J. Chem. Phys. 144, 204115 (2016)], has been approved for the DCB-Ar complexes. Simplified SAPT models based on these relations have been employed to explain physical reasons for differences in the structures and the binding energies of DCB-Ar isomers. It is shown that the equilibrium distance of Ar to DCB plane and the binding energy are determined mainly by dispersion energy. The shift of Ar toward Cl is caused by both exchange and dispersion terms.

Stability and Interconversion of Acetylcholine Conformers

The gas phase structures, energetics, and interconversion pathways of five lowest energy conformers of acetylcholine were examined employing the B3LYP, MP2, and CCSD(T) methods in conjunction with diverse basis sets including the correlation consistent aug-cc-pVDZ and aug-cc-pVTZ basis sets. It is found that use of adequate basis set containing proper polarization and diffuse functions capable of describing the floppy potential energy surface of acetylcholine is important in correctly predicting the relative stability of these conformers. The interconversion pathways and barrier heights between these conformers were elucidated by examining the potential energy surface for torsional motion, which also manifested the presence of chiral conformations of acetylcholine corresponding to the original conformations. On the basis of high level electronic energy calculations and thermal contribution analysis, four lowest energy conformers appear to be populated in the energy range of less than 1 kcal/mol at room temperature.

An efficient methodology to study cyclodextrin clusters: application to α-CD hydrated monomer, dimer, trimer and tetramer

The hydrated α-cyclodextrin (α-CD) clusters resulting from the following process: nα-CD + n(H2O)6 → α-CDn · 6nH2O, with n = 1, 2, 3, 4, have been investigated using semiempirical (PM3), ab initio Hartree-Fock and Density Functional Theory (BLYP functional) levels of theory. The largest structure containing 576 atoms and 5,760 contracted basis functions (6-31G(d,p) basis set) poses as a considerable hard task for quantum chemical calculations. As the number of basis function increases rapidly with the cluster size, an alternative procedure to make the calculations feasible is certainly welcome, in order to perform BLYP calculations with an adequate basis set. Through the aid of a computer program that we developed, it became of practical use the selection of atom by atom basis sets, using the common chemical sense, enabling quantum mechanical calculations to be performed for very large molecular interacting systems (inclusion complexes), at an affordable computational cost. In this article we show how an appropriate selection of basis functions, leaving the CHn groups with a minimal basis set and the oxygen atoms (and OH groups) with a better quality basis set, lower considerably the computational cost with no significant loss in the calculated interaction energies. A regular pattern is observed for α-CD hydrated monomer, dimer, trimer and tetramer, therefore adding support to the use of this procedure when studying larger hydrogen bonded clusters where electron correlation effects are important. We show that the procedure reported here enables DFT calculations for hydrated cyclodextrin using basis set up to the 6-311++G(3df,3pd) triple zeta quality .

Comparison of density functionals for energy and structural differences between the high- [5T2g:(t2g)4(eg)2] and low- [1A1g:(t2g)6(eg)] spin states of iron(II) coordination compounds. II. More functionals and the hexaminoferrous cation, [Fe(NH3)6]2+

The ability of different density functionals to describe the structural and energy differences between the high- [(5)T(2g):(t(2g))(4)(e(g))(2)] and low- [(1)A(1g):(t(2g))(6)(e(g))(0)] spin states of small octahedral ferrous compounds is studied. This work is an extension of our previous study of the hexaquoferrous cation, [Fe(H(2)O)(6)](2+), [J. Chem. Phys. 120, 9473 (2004)] to include a second compound-namely, the hexaminoferrous cation, [Fe(NH(3))(6)](2+)-and several additional functionals. In particular, the present study includes the highly parametrized generalized gradient approximations (GGAs) known as HCTH and the meta-GGA VSXC [which together we refer to as highly parametrized density functionals (HPDFs)], now readily available in the GAUSSIAN03 program, as well as the hybrid functional PBE0. Since there are very few experimental results for these molecules with which to compare, comparison is made with best estimates obtained from second-order perturbation theory-corrected complete active space self-consistent field (CASPT2) calculations, with spectroscopy oriented configuration interaction (SORCI) calculations, and with ligand field theory (LFT) estimations. While CASPT2 and SORCI are among the most reliable ab initio methods available for this type of problem, LFT embodies many decades of empirical experience. These three methods are found to give coherent results and provide best estimates of the adiabatic low-spin-high-spin energy difference, DeltaE(LH) (adia), of 12 000-13 000 cm(-1) for [Fe(H(2)O)(6)](2+) and 9 000-11 000 cm(-1) for [Fe(NH(3))(6)](2+). All functionals beyond the purely local approximation produce reasonably good geometries, so long as adequate basis sets are used. In contrast, the energy splitting, DeltaE(LH) (adia), is much more sensitive to the choice of functional. The local density approximation severely over stabilizes the low-spin state with respect to the high-spin state. This "density functional theory (DFT) spin pairing-energy problem" persists, but is reduced, for traditional GGAs. In contrast the hybrid functional B3LYP underestimates DeltaE(LH) (adia) by a few thousands of wave numbers. The RPBE GGA of Hammer, Hansen, and Norskov gives good results for DeltaE(LH) (adia) as do the HPDFs, especially the VSXC functional. Surprisingly the HCTH functionals actually over correct the DFT spin pairing-energy problem, destabilizing the low-spin state relative to the high-spin state. Best agreement is found for the hybrid functional PBE0.

Density functional theory calculation of indirect nuclear magnetic resonance spin-spin coupling constants in C(70).

We calculate NMR spin-spin coupling constants in the C70 fullerene by means of density functional theory. We show that using a hybrid density functional (B3LYP) and an adequate basis set (cc-pCVDZ-sd), excellent agreement with experimental values can be achieved for one-bond couplings. These benchmark calculations suggest that theoretical predictions of NMR spin-spin couplings can be extremely valuable for discerning structural information of fullerenes.

Effect of correlating core orbitals in calculations of nuclear spin–spin couplings

Electron correlation effects on nuclear spin–spin coupling tensors arising from core-valence interaction were investigated with ab initio calculations based on multiconfigurational self-consistent field (MCSCF) reference states, an adequate basis set, and large restricted active spaces. Calculations of first and second-row hydrides were performed to examine the effect of including the core and semicore orbitals in the active molecular orbital space. The effects of using a multireference wave function instead of a single-reference one, as well as different numbers of electrons in the virtual orbitals, were considered. In second-row hydrides, the inclusion of semicore orbitals is found to be necessary for accurate calculations of spin–spin couplings involving the heavy nucleus. A smaller but nonnegligible effect is observed also for the hydrogen–hydrogen coupling. Comparison is made with nuclear shielding and electric field gradient, for which the effect is considerably smaller. Recommendations for wave functions for calculations of spin–spin couplings are given.

Parallel Douglas–Kroll energy and gradients in NWChem: Estimating scalar relativistic effects using Douglas–Kroll contracted basis sets

A parallel implementation of the spin-free one-electron Douglas–Kroll–Hess (DKH) Hamiltonian in NWChem is discussed. An efficient and accurate method to calculate DKH gradients is introduced. It is shown that the use of a standard (nonrelativistic) contracted basis set can produce erroneous results for elements beyond the first row elements. The generation of DKH contracted cc-pVXZ(X=D,T,Q,5) basis sets for H, He, B–Ne, Al–Ar, and Ga–Br is discussed. The effect of DKH at the Hartree–Fock level on the bond distances, vibrational frequencies, and total dissociation energies for CF4, SiH4, SiF4, and Br2CO is discussed. It is suggested that the predominant effect of the scalar relativistic correction on the total dissociation energy can be calculated at the Hartree–Fock level if an adequate basis set is used.

The problem of an atom inside a cavity in an infinite isotropic medium

The problem of a fluctuating atomic or molecular dipole inside a hollow spherical cavity in a homogeneous, isotropic, linear but non-local medium is examined. The difficulty due to the infinite extension of the medium is overcome by solving first, by use of an adequate basis set, the case of a medium limited by a concentric outer sphere of large radius (respecting the symmetry of the problem). It is then shown that when this radius tends to infinity, the results obtained in the quasi-static approximation, and in particular the reflection factors involved in the response field, take definite limits. These results, similar to but different from those obtained with a dipole outside a filled sphere, give a rigorous background to further extend the efficient ‘propagator method’ to the case of atomic or molecular systems confined in hollow cavities, or bubbles of finite thickness, of a micro- or nanometer size.

Using fuzzy set theory to assess basis set quality

An algorithm, based on Zadeh's fuzzy set theory, to make an adequate basis set choice to compute simultaneously a number of molecular properties within Roothaan's algebraic approximation is presented. Its usefulness is illustrated by analyzing fuzzy set predictions and actual results from molecular calculations on NiH2, a system for which it has been recently shown that the choice of an adequate basis set is important.

QUALITY: A program to assess basis set quality

A program to analyze in detail the quality of basis sets is presented. The information provided by the application of a wide variety of (atomic and/or molecular) quality criteria is processed by using a methodology that allows one to determine the most appropriate quality test to select a basis set to compute a given (atomic or molecular) property. Fuzzy set theory is used to choose the most adequate basis set to compute simultaneously a set of properties.

Calculation of positron 2D-ACAR spectra and lifetimes in molecular crystals

Positron 2D-ACAR (two-dimensional angular correlation of annihilation radiation) spectra and lifetimes in molecular crystals have been theoretically calculated. The obtained results are in good agreement with the existing experiments when an adequate basis set and electron-positron correlation are used in the calculation.

Theoretical study of the satellite structure in the valence photoelectron spectra of the second and third row hydrides

The adequacy of the 2 h-1 p CI scheme for the interpretation of the valence ionization shake-up was first analysed in neon and argon, paying special attention to the choice of an adequate basis set, the explicit inclusion of relaxation by the use of relaxed orbitals and the correlation of the ground state. The scheme was then applied to the calculation of the shake-up of the isoelectronic series of hydrides: i.e. HF, H 20, NH 3 and CH 4; HCl, H 2S, PH 3 and SiH 4. The results obtained compare well with experiment and previous calculations, showing that in the hydrides the shakeup is dominated by the same effects as in neon and argon, and providing a consistent interpretation of the available experimental data.

The calculation of potential-energy surfaces for molecular ions

A review is given of the application of the multi-reference configuration interaction method for the ab initio calculation of potential-energy surfaces for molecular ions. The importance of using adequate basis sets and of choosing suitable sets of reference configurations is discussed. Recent calculations for SiH+ and SiH+2 are outlined in the context of their relevance to recent spectroscopic and dynamical experiments.

Basis set effects on spectroscopic constants for C2 and Si2 and the symmetry dilemma in the Xα model

In an attempt to perform thorough and accurate linear combination of atomic orbitals (LCAO) Xα, calculations on C2 and Si2, the effects of basis set composition on the computed spectroscopic constants are investigated for the first time. The questions of how to tell if an adequate basis set has been found and what Xα state corresponds to the lowest state of 1Σ+g symmetry which involves strong electron correlation effects are addressed. With the larger bases, general agreement with experiment and previous density functional calculations are obtained. Remarkable agreement with the configuration interaction (CI) calculations of Bruna et al. on Si2 is obtained if the fractional occupation number method of Slater et al. is used.