Equilibrium Dissociation Energies Research Articles

Ab initiostudy ofMXen+(M=Cu, Ag, and Au;n=1,2)

The equilibrium geometries, vibrational frequencies, dissociation energies, and populations of the title species were studied at Hartree-Fock (HF), second-order M\o{}ller-Plesset (MP2), and coupled-cluster singles-doubles (triples) [CCSD(T)] levels. The electron correlation effects and relativistic effects on the geometry and stability were investigated at the CCSD(T) level. Both effects stabilize title species. The populations analyses show that $M\text{-Xe}$ bonding is dominated by electrostatic interactions and the best theoretical estimate of the dissociation energies are 1.104 and 2.260 eV for ${\text{AuXe}}^{+}$ and ${\text{AuXe}}_{2}^{+}$, respectively. The Cu and Ag are weakly bonded to Xe compared to Au.

The structure and potential energy function of PdCO molecule

Density functional method(B3LPY) has been used to optimize the possible structures of PdC，PdO and PdCO molecules with contracted valence basis set (LANL2DZ) for Pd atom and the AUG-cc-pVTZ basis set for C and O atoms respectively.It was found that the ground state of PdC molecule is 1Σ，whose equilibrium nuclear distance and dissociation energy are RPdC=0.17285nm and 4.919eV, respectively.The ground state of PdO molecule is 3Π with equilibrium geometry RPdO=0.18546nm and dissociation energy De=2.455eV. The ground state of the linear Pd—C≡O (C∞v) is 1Σ+ and the configuration and dissociation energy are RPdC=0.18721nm，RCO=0.11427nm and 12.563eV, respectively. At the same time， another metastable structure Pd—O≡C(C∞v) was found. Its equilibrium geometry and dissociation energy are RCO=0.11336nm， RPdO=0.23001nm and 10.937eV, respectively.The possible dissociation limit of PdCO molecule is determined.The analytical potential energy function for PdCO molecule has been obtained from the many-body expansion theory.The contour of the potential energy surface sheds light on the accurate structure and dissociative energy for PdCO molecule.Furthermore, the molecular static reaction pathway based on this potential energy function is investigated.

The confirmation of accurate combination of functional and basis set for transition‐metal dimers: Fe2, Co2, Ni2, Ru2, Rh2, Pd2, Os2, Ir2, and Pt2

AbstractEight kinds of density functionals named B3LYP, PBE1PBE, B1B95, BLYP, BP86, G96PW91, mPWPW91, and SVWN along with two different valence basis sets (LANL2DZ and CEP‐121g) are employed to study the transition‐metal dimers for the elements of group VIII. By comparing the equilibrium bond distances, vibrational frequencies, and dissociation energies of the ground state of these dimers with the available experimental values and theoretical data, we show that the “pure” DFT methods (G96PW91, BLYP, and BP86) with great‐gradient approximation always give better results relative to the hybrid HF/DFT schemes (B3LYP, PBE1PBE, and B1B95). The striking case found by us is that the G96PW91 functional, which is not tested in previous systemic studies, always predicts the dissociation energy to be well. The Ru2 and Os2 dimers are sensitive to not only the functionals employed but also the valence basis sets adopted. The natural bond orbital population is analyzed, and the molecular orbitals of the unpaired electrons are determined. Furthermore, our results indicate that the s and d orbitals of these dimers always hybridize with each other except for Rh2 and Pt2 molecules. And by analyzing the electron configuration of the bonding atom, the dissociation limit of the ground state is obtained. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Ground State Potential Energy Curve and Dissociation Energy of MgH

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v''=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v''=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy.

Calculated spectroscopic and electric properties of the alkali metal-ammonia complexes from Kn–NH3 to Frn–NH3 (n=,+1)

The newly developed Stuttgart small-core scalar relativistic pseudopotentials for the alkali metals are used to study spectroscopic and electric properties of the heavier alkali metal-ammonia complexes from K(n)-NH(3) to Fr(n)-NH(3) (n=0,+1) at the second-order Moller-Plesset (MP2) and coupled cluster [CCSD(T)] levels of theory. Equilibrium geometries and dissociation energies computed at the MP2 level are in reasonable agreement with their CCSD(T) counterparts, whereas for the dipole polarizabilities MP2 is not performing well overestimating significantly electron correlation effects. The bond distances increase monotonically with increasing mass of the metal atom as relativistic effects are small in these systems. However, the dipole polarizabilities are more sensitive to such effects and we find a decrease in this property from Cs-NH(3) to Fr-NH(3). Combination of CCSD(T) harmonic frequencies and MP2 anharmonic corrections obtained from a perturbative vibrational treatment leads to fundamental frequencies in good agreement with experimental results obtained by Suzer and Andrews [J. Am. Chem. Soc. 109, 300 (1986)]. We also present the results of variational calculations with a three-dimensional vibrational Hamiltonian, making use of CCSD(T) potential energy and electric dipole moment surfaces. Complexation of NH(3) to the metal causes a strong infrared intensification of the symmetric NH(3) stretching mode in the neutral complexes, which is absent in the charged species.

Potential energy surfaces of ozone in the ground state

Equilibrium parameters of ozone, such as equilibrium geometry structure parameters, force constants and dissociation energy are presented by CBS-Q ab initio calculations. The calculated equilibrium geometry structure parameters and energy are in agreement with the corresponding experimental values. The potential energy function of ozone with a C2v symmetry in the ground state is described by the simplified Sorbie–Murrell many-body expansion potential function according to the ozone molecule symmetry. The contour of bond stretching vibration potential of an O3 in the ground state, with a bond angle (θ) fixed, and the contour of O3 potential for O rotating around O1−O (R1), with O1−O bond length taken as the one at equilibrium, are plotted. Moreover, the potentials are analysed.

The molecular structure and the analytical potential energy function of S2−and S3−

In this paper, the equilibrium geometry, harmonic frequency and dissociation energy of S2− and S3− have been calculated at QCISD/6–311++G(3d2f) and B3P86/6–311++G(3d2f) level. The S2− ground state is of 2∏g, the S3− ground state is of 2B1 and S3− has a bent (C2V) structure with an angle of 115.65° The results are in good agreement with these reported in other literature. For S3− ion, the vibration frequencies and the force constants have also been calculated. Base on the general principles of microscopic reversibility, the dissociation limits has been deduced. The Murrell-Sorbie potential energy function for S2− has been derived according to the ab initio data through the least-squares fitting. The force constants and spectroscopic data for S2− have been calculated, then compared with other theoretical data. The analytical potential energy function of S3− have been obtained based on the many-body expansion theory. The structure and energy can correctly reappear on the potential surface.

Ab initio study of spectroscopic properties of RgCl (Rg=He, Ne, Ar, Kr) and their anions

Spectroscopic properties of HeCl, NeCl, ArCl, KrCl and their anions HeCl−, NeCl−, ArCl− and KrCl− in their ground state have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods. These neutral molecules and their anions are weakly bound and their spectroscopic constants have been estimated using a method developed recently for calculating the spectroscopic constants of weakly bound molecule in Lennard–Jones potential. The net attractive force and the distance at which the net attractive force is greatest, have been calculated to get the physical picture. Most of the spectroscopic constants are first predicted. The calculated equilibrium bond length, dissociation energy and harmonic frequency agree very well with the experimental and theoretical values wherever available.

MRCI study on the ground and low-lying excited states of lutetium dimer

The multi-reference configuration interaction (MRCI) method and effective-core-potential (ECP) basis set have been used to calculate the equilibrium geometries, dissociation energies and potential energy curves (PECs) of nine states of Lu 2 dimer. The analytical potential energy functions (APEFs) of these states have been fitted using Murrell–Sorbie (MS) function and least square fitting method. Based on this, the spectroscopic parameters of each state are calculated and are compared with the theoretical and the experimental values available at present. The ground state of this dimer is determined by considering both the total energy and the spectroscopic parameters. The vibrational levels for each state of Lu 2 are determined by solving Schrödinger equation of nuclear motion.

Spectroscopic properties of Zn 2, ZnHe, ZnNe and ZnAr van der Waals molecules: A CCSD(T) study

Spectroscopic properties of Zn 2, ZnHe, ZnNe and ZnAr van der Waals molecules have been studied using CCSD(T) method. The spectroscopic constants are estimated from our newly developed method for calculating the spectroscopic constants of weakly bound molecule in Lennard–Jones potential. Most of the spectroscopic constants are first predicted. The equilibrium bond length, harmonic frequency and dissociation energy agree very well with the experimental values.

The structure and potential energy function of B2C(1A1) and BC2(2A′)

Quadratic configuration interaction method including single and duble substitutions has been used to optimize the possible ground-state structures of B2C and BC2 molecules with the 6-311++G(d, f) and 6-311G(df, pd) basis set. The results show that the ground state of B2C molecule is of C2v symmetry and of 1A1 state, the ground state of BC2 molecule is of Cs symmetry and of 2A′ state. And the equilibrium geometry, dissociation energy, harmonic frequency and force constant have been calculated. The potential energy functions of B2C and BC2 have been derived from the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules. Molecular reaction kinetics of B+BC→B2C and B+CC→BC2 based on the potential energy functions is discussed briefly.

Are the program packages for molecular structure calculations really black boxes?

In this communication it is shown that the widely held opinion that compact program packages for quantum-mechanical calculations of molecular structure can safely be used as black boxes is completely wrong. In order to illustrate this, the results of computations of equilibrium bond lengths, vibrational frequencies and dissociation energies for all homonuclear diatomic molecules involving the atoms from the first two rows of the Periodic Table, performed using the Gaussian program package are presented. It is demonstrated that the sensible use of the program requires a solid knowledge of quantum chemistry.

MRCI potential curves and analytical potential energy functions of the low-lying excited states (1∏，3∏) of ZnHg

The multireference configuration interaction (MRCI) electronic energy calculations with effective core potentials have been carried out for two low-lying excited states (1∏,3∏) of ZnHg dimer. Potential energy curves (PECs) are generated. The PECs are fitted to analytical potential energy functions (APEFs) using the Murrel-Sorbie potential function. The computational equilibrium interatomic distances and dissociation energies are compared with the theoretical values available in the literature. Some important spectroscopic parameters are calculated. Based on the PECs, the vibrational levels of the two states are predicted by solving Schrdinger equation of nuclear motion.

The employment of relativistic adapted Gaussian basis sets in Douglas–Kroll–Hess scalar calculations with diatomic molecules

The prolapse-free relativistic adapted Gaussian basis sets (RAGBSs), developed by our research group on the basis of the four-component approach, are used for the first time in Douglas–Kroll–Hess 2nd order scalar relativistic calculations (DKH2) of simple diatomic molecules containing Hydrogen and the halogens from Fluorine up to Iodine: HX and X 2, where X = F, Cl, Br, and I. To this end, the RAGBSs were contracted with the general contraction scheme to triple-, quadruple-, and quintuple-zeta sets. Polarization functions were also added to the basis sets by optimization with the configuration interaction method including single and double excitations into the DKH2 environment, DKH2-CISD. The molecular properties were then calculated with the coupled cluster electronic correlation treatment and the DKH2 scalar relativistic method, DKH2-CCSD(T), and indicated that our RAGBSs should be contracted as quadruple-zeta basis sets. The results achieved with the DKH2-CCSD(T) calculations and the selected quadruple-zeta RAGBSs are able to reproduce the experimental data of equilibrium distances, dissociation energies, and harmonic vibrational frequencies with root-mean-square (rms) errors of 0.015 Å, 3.6 kcal mol −1, and 21.7 cm −1, respectively.

Chemically Accurate Thermochemistry of Cadmium: An ab Initio Study of Cd + XY (X = H, O, Cl, Br; Y = Cl, Br)

Using a composite coupled cluster method employing sequences of correlation consistent basis sets for complete basis set (CBS) extrapolations and with explicit treatment of core-valence correlation and scalar and spin-orbit relativistic effects, the 0 K enthalpies of a wide range of cadmium-halide reactions, namely, Cd + (HCl, HBr, ClO, BrO, Cl2, BrCl, Br2) have been determined to an estimated accuracy of +/-1 kcal/mol. In addition, accurate equilibrium geometries, harmonic frequencies, and dissociation energies have been calculated at the same level of theory for all the diatomic (e.g., CdH, CdO, CdCl, CdBr) and triatomic (CdHCl, CdHBr, CdClO, CdBrO, CdCl2, CdBrCl, CdBr2) species involved in these reactions, some for the very first time. Like their mercury analogues, all of the abstraction reactions are predicted to be endothermic, while the insertion reactions are strongly exothermic with the formation of stable linear, Cd-centric complexes. With the exception of CdH and the reactions involving this species, the present results for the remaining Cd-containing systems are believed to be the most accurate to date.

Many‐body Expanded Analytical Potential Energy Function for Ground State PuOH Molecule

AbstractUsing the density functional method B3LYP with relativistic effective core potential (RECP) for Pu atom, the low‐lying excited states (4Σ+, 6Σ+, 8Σ+) for three structures of PuOH molecule were optimized. The results show that the ground state is X6Σ+of the linear Pu‐O‐H (C∞v), its corresponding equilibrium geometry and dissociation energy are RPu–O=0.20595 nm, RO–H=0.09581 nm and −8.68 eV, respectively. At the same time, two other metastable structures [PuOH (Cs) and H‐Pu‐O (C∞v)] were found. The analytical potential energy function has also been derived for whole range using the many‐body expansion method. This potential energy function represents the considerable topographical features of PuOH molecule in detail, which is adequately accurate in the whole potential surface and can be used for the molecular reaction dynamics research.

Quantum Monte Carlo calculations of the dissociation energy of the water dimer

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy D(e) of the water dimer. The dissociation energy measured experimentally, D(0), can be estimated from D(e) by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas et al., [J. Chem. Phys. 113, 6687 (2000)] leads to D(e)=5.00+/-0.7 kcal mol(-1), although the result Curtiss et al., [J. Chem. Phys. 71, 2703 (1979)] D(e)=5.44+/-0.7 kcal mol(-1), which uses an earlier estimate of the vibrational energy, has been widely quoted. High-level coupled cluster calculations Klopper et al., [Phys. Chem. Chem. Phys. 2, 2227 (2000)] have yielded D(e)=5.02+/-0.05 kcal mol(-1). In an attempt to shed new light on this old problem, we have performed all-electron DMC calculations on the water monomer and dimer using Slater-Jastrow wave functions with both Hartree-Fock approximation (HF) and B3LYP density functional theory single-particle orbitals. We obtain equilibrium dissociation energies for the dimer of 5.02+/-0.18 kcal mol(-1) (HF orbitals) and 5.21+/-0.18 kcal mol(-1) (B3LYP orbitals), in good agreement with the coupled cluster results.

Structure and analytical potential energy function for the ground state of the BCx(x=0, –1)

In this paper, the electronic states of the ground states and dissociation limits of BC and BC− are correctly determined based on group theory and atomic and molecular reaction statics. The equilibrium geometries, harmonic frequencies and dissociation energies of the ground state of BC and BC− are calculated by using density function theory and quadratic CI method including single and double substitutions. The analytical potential energy functions of these states have been fitted with Murrell–Sorbie potential energy function from our ab initio calculation results. The spectroscopic data (αe, ωe and ωeχe) of each state is calculated via the relation between analytical potential energy function and spectroscopic data. All the calculations are in good agreement with the experimental data.

Ab initio calculation of accurate dissociation energy, potential energy curve and dipole moment function for the A 1 Σ + state 7 LiH molecule

The reasonable dissociation limit of the A1Σ+ state 7LiH molecule is obtained. The accurate dissociation energy and the equilibrium geometry of this state are calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space for the first time. The whole potential energy curve and the dipole moment function for the A1Σ+ state are calculated over a wide internuclear separation range from about 0.1 to 1.4 nm. The calculated equilibrium geometry and dissociation energy of this potential energy curve are of Re=0.2487 nm and De=1.064 eV, respectively. The unusual negative values of the anharmonicity constant and the vibration-rotational coupling constant are of ωeχe=–4.7158cm−1 and αe=–0.08649cm−1, respectively. The vertical excitation energy from the ground to the A1Σ+ state is calculated and the value is of 3.613 eV at 0.15875 nm (the equilibrium position of the ground state). The highly anomalous shape of this potential energy curve, which is exceptionally flat over a wide radial range around the equilibrium position, is discussed in detail. The harmonic frequency value of 502.47cm−1 about this state is approximately estimated. Careful comparison of the theoretical determinations with those obtained by previous theories about the A1Σ+ state dissociation energy clearly shows that the present calculations are much closer to the experiments than previous theories, thus represents an improvement.

The molecular structure and potential energy function of the ground state of BH2 molecule

The density function (B3P86) method with relativistic effective core potential has been used to optimize the structure of the ground state of BH2,BH2+ and BH2- molecules or ions,which are angular H-B-H, whose equilibrium nuclear distance and dissociation energy respectively are RBH=RBH=0.11899nm,RHH=0.21514nm，and 7.752eV; RBH=RBH=0.12896nm,RHH=0.14223nm; RBH=RBH=0.12037nm,RHH=0.21087nm. The analytic potential energy function of the ground state of BH2(2A′) has been derived by the many-body expansion theory using the equilibrium geometry structure parameters,dissociation energy and force constants,which is successfully used for describing the equilibrium geometry of BH2(2A′).