Publications (21)84.36 Total impact
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ABSTRACT: In this report, we summarize and describe the recent unique updates and additions to the Molcas quantum chemistry program suite as contained in release version 8. These updates include natural and spin orbitals for studies of magnetic properties, local and linear scaling methods for the DouglasKrollHess transformation, the generalized active space concept in MCSCF methods, a combination of multiconfigurational wave functions with density functional theory in the MCPDFT method, additional methods for computation of magnetic properties, methods for diabatization, analytical gradients of state average complete active space SCF in association with density fitting, methods for constrained fragment optimization, largescale parallel multireference configuration interaction including analytic gradients via the interface to the Columbus package, and approximations of the CASPT2 method to be used for computations of large systems. In addition, the report includes the description of a computational machinery for nonlinear optical spectroscopy through an interface to the QM/MM package Cobramm. Further, a module to run molecular dynamics simulations is added and two surface hopping algorithms are included to enable nonadiabatic calculations. Finally, we report on the subject of improvements with respects to alternative file options and parallelization. © 2015 Wiley Periodicals, Inc.  [Show abstract] [Hide abstract]
ABSTRACT: The bond dissociation energy of a series of metallocenium ions, i.e., the energy difference of the reaction MCp2+ >(+) MCp2 > MCp+ + Cp (with M = Ti, V, Cr, Mn, Fe, Co, and Ni), was studied by means of multiconfigurational perturbation theory (CASPT2, RASPT2, NEVPT2) and restricted coupled cluster theory (CCSD(T)). From a comparison between the results obtained from these different methods, and a detailed analysis of their treatment of electron correlation effects, a set of MCp+Cp binding energies are proposed with an accuracy of 5 kcal/mol. The computed results are in good agreement with the experimental data measured by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy but disagree with the more recent threshold collisioninduced dissociation (TCID) experiments.  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the geometry and singlettriplet energy difference of two mononuclear Ni(2+) models related to the active site in [NiFe] hydrogenase. Multiconfigurational secondorder perturbation theory based on a complete activespace wavefunction with an active space of 12 electrons in 12 orbitals, CASPT2(12,12), reproduces experimental bond lengths to within 1 pm. Calculated singlettriplet energy differences agree with those obtained from coupledcluster calculations with single, double and (perturbatively treated) triple excitations (CCSD(T)) to within 12 kJ mol(1). For a bimetallic model of the active site of [NiFe] hydrogenase, the CASPT2(12,12) results were compared with the results obtained with an extended active space of 22 electrons in 22 orbitals. This is so large that we need to use restricted activespace theory (RASPT2). The calculations predict that the singlet state is 4857 kJ mol(1) more stable than the triplet state for this model of the NiSIa state. However, in the [NiFe] hydrogenase protein, the structure around the Ni ion is far from the squareplanar structure preferred by the singlet state. This destabilises the singlet state so that it is only ∼24 kJ mol(1) more stable than the triplet state. Finally, we have studied how various density functional theory methods compare to the experimental, CCSD(T), CASPT2, and RASPT2 results. Semilocal functionals predict the best singlettriplet energy differences, with BP86, TPSS, and PBE giving mean unsigned errors of 1213 kJ mol(1) (maximum errors of 2531 kJ mol(1)) compared to CCSD(T). For bond lengths, several methods give good results, e.g. TPSS, BP86, and M06, with mean unsigned errors of 2 pm for the bond lengths if relativistic effects are considered.  [Show abstract] [Hide abstract]
ABSTRACT: Static excitedstate polarisabilities and hyperpolarisabilities of three Ru(II) ammine complexes are computed at the density functional theory (DFT) and several correlated ab initio levels. Most accurate modelling of the low energy electronic absorption spectrum is obtained with the hybrid functionals B3LYP, B3P86 or M06 for the complex [Ru(II) (NH3 )5 (MeQ(+) )](3+) (MeQ(+) =Nmethyl4,4'bipyridinium, 3) in acetonitrile. The match with experimental data is less good for [Ru(II) (NH3 )5 L](3+) (L=Nmethylpyrazinium, 2; Nmethyl4{E,E4(4pyridyl)buta1,3dienyl}pyridinium, 4). These calculations confirm that the first dipole allowed excited state (FDAES) has metaltoligand chargetransfer (MLCT) character. Both the solution and gasphase results obtained for 3 by using B3LYP, B3P86 or M06 are very similar to those from restricted activespace SCF secondorder perturbation theory (RASPT2) with a very large basis set and large active space. However, the timedependent DFT λmax predictions from the longrange corrected functionals CAMB3LYP, LCωPBE and wB97XB and also the fully ab initio resolution of identity approximate coupledcluster method (gasphase only) are less accurate for all three complexes. The ground state (GS) twostate approximation first hyperpolarisability β2SA for 3 from RASPT2 is very close to that derived experimentally via hyperRayleigh scattering, whereas the corresponding DFTbased values are considerably larger. The β responses calculated by using B3LYP, B3P86 or M06 increase markedly as the πconjugation extends on moving along the series 2→4, for both the GS and FDAES species. All three functionals predict substantial FDAES β enhancements for each complex, increasing with the πconjugation, up to about sevenfold for 4. Also, the computed second hyperpolarisabilities γ generally increase in the FDAES, but the results vary between the different functionals.  [Show abstract] [Hide abstract]
ABSTRACT: Because of its excellent properties in nanotechnology applications, atomic layer deposition of ruthenium (Ru) has been the subject of numerous experimental studies. Recently, two different Ru precursors were compared for plasmaenhanced atomic layer deposition (PEALD) of Ru, and their reactivity was found to be different. Inhibition was observed for bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2), while nearly linear growth behavior was observed for (methylcyclopentadienylpyrrolyl)ruthenium (Ru(MeCp)Py). To understand this difference in reactivity, we investigate the adsorption of RuCp2 and RuCpPy (i.e., without substituents) on a TiN surface using calculations based on periodic boundary conditions density functional theory (DFT) combined with experiments based on Rutherford backscattering spectroscopy (RBS). The calculations demonstrate that the RuCpPy precursor chemisorbs on the TiN(100) surface while the RuCp2 precursor only physisorbs. We propose a reaction mechanism for the chemisorption of RuCpPy. The area density of the calculated RuCpPy surface species is compared with the experimental values from RBS. The impact of a Hplasma is also investigated. The DFT calculations and experimental results from RBS provide insight into the adsorption processes of the RuCpPy and RuCp2 precursors on the TiN(100) surface.  [Show abstract] [Hide abstract]
ABSTRACT: Ligandfield and chargetransfer spectra of Nheterocyclic pentacyanoferrate(II) complexes [Fe(CN)5L]n− were investigated using multiconfigurational perturbation theory. The spectrum of [Fe(CN)5(py)]3– was studied in detail under vacuum and in the following polarizable continuum model (PCM) simulated solvents: acetone, acetonitrile, dimethylsulfoxide (DMSO), ethanol, methanol, and water. The ligandfield states proved to be rather insensitive to the solvent environment, whereas much stronger solvent effects were observed for the chargetransfer (CT) transitions. The nature of the intense band was confirmed as a metaltoligand charge transfer originating from a 3dxz → πb1* (L)orbital transition. The difference between the calculated and experimental transition energy of this CT transition is minimal for aprotic solvents, but increases strongly with the solvent proton donor ability in the protic solvents. In an attempt to improve the description of this CT state, up to 14 solvent molecules were explicitly included in the quantum model. In DMSO, the spectra of complexes with ligands L (where L is pyridine, 4picoline, 4acetylpyridine, 4cyanopyridine, pyrazine, and Nmethylpyrazinium) correlate very well with the experiment.  [Show abstract] [Hide abstract]
ABSTRACT: In this work, we present a parallel approach to complete and restricted active space secondorder perturbation theory, (CASPT2/RASPT2). We also make an assessment of the performance characteristics of its particular implementation in the Molcas quantum chemistry programming package. Parallel scaling is limited by memory and I/O bandwidth instead of available cores. Significant time savings for calculations on large and complex systems can be achieved by increasing the number of processes on a single machine, as long as memory bandwidth allows, or by using multiple nodes with a fast, lowlatency interconnect. We found that parallel efficiency drops below 50% when using 816 cores on the sharedmemory architecture, or 1632 nodes on the distributedmemory architecture, depending on the calculation. This limits the scalability of the implementation to a moderate amount of processes. Nonetheless, calculations that took more than 3 days on a serial machine could be performed in less than 5 h on an InfiniBand cluster, where the individual nodes were not even capable of running the calculation because of memory and I/O requirements. This ensures the continuing study of larger molecular systems by means of CASPT2/RASPT2 through the use of the aggregated computational resources offered by distributed computing systems. © 2013 Wiley Periodicals, Inc.  [Show abstract] [Hide abstract]
ABSTRACT: RuCp2 (ruthenocene) and RuCpPy (cyclopentadienyl pyrrolyl ruthenium) complexes are used in ruthenium (Ru) atomic layer deposition (ALD) but exhibit a markedly different reactivity with respect to the substrate and coreactant. In search of an explanation, we report here the results of a comparative study of the heterolytic and homolytic dissociation enthalpy of these two ruthenium complexes, making use of either density functional theory (DFT) or multiconfigurational perturbation theory (CASPT2). While both methods predict distinctly different absolute dissociation enthalpies, they agree on the relative values between both molecules. A reduced heterolytic dissociation enthalpy is obtained for RuCpPy compared to RuCp2, although the difference obtained from CASPT2 (19.9 kcal/mol) is slightly larger than the one obtained with any of the DFT functionals (around 17 kcal/mol). Both methods also agree on the more pronounced stability of the Cp− ligand in RuCpPy than in RuCp2 (by around 9 kcal/mol with DFT and by 6 kcal/mol with CASPT2).  [Show abstract] [Hide abstract]
ABSTRACT: The MCD spectra of mesotriarylsubporphyrins show a sign anomaly which is correlated with the acceptor properties of the aryl substituent. From the spectra, magnetic moments of the excited states are determined. In the context of a simplified orbital model, the sign change is attributed to the quenching of the magnetic moment of the LUMO by acceptor orbitals of the substituent. The actual calculation of this moment presents a major challenge to computational methods. It is shown that wave function techniques based on CASSCF underestimate the covalency effects that are responsible for the quenching. In contrast, a CI method based on DFT orbitals yields excellent results, which fully support the orbital model.  [Show abstract] [Hide abstract]
ABSTRACT: The heterolytic dissociation enthalpy of a series of firstrow metallocenes M(C5H5)(2), M = V, Mn, Fe, and Ni, was studied by (restricted) multiconfigurational perturbation theory and density functional theory. The results were compared directly to the experimental values, taking into account all necessary contributions to the relative energy. Of the tested fimctionals, B3LYP performs best in reproducing the binding energy, while the PBE0 functional gives the best structures. High quality multiconfigurational perturbation calculations were also carried out, demonstrating the superior performance of a larger, restricted active space. The spin crossover behavior of manganocene is correctly predicted by multiconfigurational perturbation theory as opposed to the three functionals B3LYP, PBE0, and M06, which (severely) overstabilize the highspin with respect to the lowspin state.  [Show abstract] [Hide abstract]
ABSTRACT: A series of model transitionmetal complexes, CrF(6), ferrocene, Cr(CO)(6), ferrous porphin, cobalt corrole, and FeO/FeO(), have been studied using secondorder perturbation theory based on a restricted active space selfconsistent field reference wave function (RASPT2). Several important properties (structures, relative energies of different structural minima, binding energies, spin state energetics, and electronic excitation energies) were investigated. A systematic investigation was performed on the effect of: (a) the size and composition of the global RAS space, (b) different (RAS1/RAS2/RAS3) subpartitions of the global RAS space, and (c) different excitation levels (out of RAS1/into RAS3) within the RAS space. Calculations with active spaces, including up to 35 orbitals, are presented. The results obtained with smaller active spaces (up to 16 orbitals) were compared to previous and current results obtained with a complete active space selfconsistent field reference wave function (CASPT2). Higly accurate RASPT2 results were obtained for the heterolytic binding energy of ferrocene and for the electronic spectrum of Cr(CO)(6), with errors within chemical accuracy. For ferrous porphyrin the intermediate spin (3)A(2g) ground state is (for the first time with a wave functionbased method) correctly predicted, while its high magnetic moment (4.4 mu(B)) is attributed to spinorbit coupling with very closelying (5)A(1g) and (3)E(g) states. The toughest case met in this work is cobalt corrole, for which we studied the relative energy of several lowlying Co (II)corrole pi radical states with respect to the Co(III) ground state. Very large RAS spaces (2533 orbitals) are required for this system, making compromises on the size of RAS2 and/or the excitation level unavoidable, thus increasing the uncertainty of the RASPT2 results by 0.10.2 eV. Still, also for this system, the RASPT2 method is shown to provide distinct improvements over CASPT2, by overcoming the strict limitations in the size of the active space inherent to the latter method.  [Show abstract] [Hide abstract]
ABSTRACT: The recently developed secondorder perturbation theory restricted active space (RASPT2) method has been benchmarked versus the wellestablished complete active space (CASPT2) approach. Vertical excitation energies for valence and Rydberg excited states of different groups of organic (polyenes, acenes, heterocycles, azabenzenes, nucleobases, and free base porphin) and inorganic (nickel atom and copper tetrachloride dianion) molecules have been computed at the RASPT2 and multistate (MS) RASPT2 levels using different reference spaces and compared with CASPT2, CCSD, and experimental data in order to set the accuracy of the approach, which extends the applicability of multiconfigurational perturbation theory to much larger and complex systems than previously. Relevant aspects in multiconfigurational excited state quantum chemistry such as the valenceRydberg mixing problem in organic molecules or the double dshell effect for firstrow transition metals have also been addressed.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper, the results are presented from a comparative study of the electronic and geometric structure of copper corroles by means of either density functional theory (DFT, using both pure and hybrid functionals) and multiconfigurational ab initio methods, starting from either a complete active space (CASSCF) or restricted active space (RASSCF) reference wave function and including dynamic correlation by means of secondorder perturbation theory (CASPT2/RASPT2). DFT geometry optimizations were performed for the lowest singlet and triplet states of copper corrole, both unsubstituted and mesosubstituted with three phenyl groups. The effect of saddling on the electronic structure was investigated by comparing the results obtained for planar (C(2v)) and saddled (C(2)) structures. With DFT, the origin of the saddling distortion is found to be dependent on the applied functional: covalent Cu 3dcorrole π interactions with pure functionals (BP86, OLYP), antiferromagnetic exchange coupling between an electron in the corrolate (C(2)) b type π orbital, and an unpaired Cu(II) 3d electron with hybrid functionals (B3LYP, PBE0). The CASPT2 results essentially confirm the suggestion from the hybrid functionals that copper corroles are noninnocent, although the contribution of diradical character to the coppercorrole bond is found to be limited to 50% or less. The lowest triplet state is calculated at 010 kcal/mol and conform with the experimental observation (variable temperature NMR) that this state should be thermally accessible.  [Show abstract] [Hide abstract]
ABSTRACT: EPR spectroscopy has proven to be an indispensable tool in elucidating the structure of metal sites in proteins. In recent years, experimental EPR data have been complemented by theoretical calculations, which have become a standard tool of many quantum chemical packages. However, there have only been a few attempts to calculate EPR g tensors for exchangecoupled systems with more than two spins. In this work, we present a quantum chemical study of structural, electronic, and magnetic properties of intermediates in the reaction cycle of multicopper oxidases and of their inorganic models. All these systems contain three copper(II) ions bridged by hydroxide or O(2) anions and their ground states are antiferromagnetically coupled doublets. We demonstrate that only multireference methods, such as CASSCF/CASPT2 or MRCI can yield qualitatively correct results (compared to the experimental values) and consider the accuracy of the calculated EPR g tensors as the current benchmark of quantum chemical methods. By decomposing the calculated g tensors into terms arising from interactions of the ground state with the various excited states, the origin of the zerofield splitting is explained. The results of the study demonstrate that a truly quantitative prediction of the g tensors of exchangecoupled systems is a great challenge to contemporary theory. The predictions strongly depend on small energy differences that are difficult to predict with sufficient accuracy by any quantum chemical method that is applicable to systems of the size of our target systems.  [Show abstract] [Hide abstract]
ABSTRACT: The accuracy of the relative spinstate energetics of three small FeII or FeIII heme models from multiconfigurational perturbation theory (CASPT2) and density functional theory with selected functionals (including the recently developed M06 and M06L functionals) was assessed by comparing with recently available coupled cluster results. While the CASPT2 calculations of spinstate energetics were found to be very accurate for the studied FeIII complexes (including FeP(SH), a model of the active site of cytochrome P450 in its resting state), there is a strong indication of a systematic error (around 5 kcal/mol) in favor of the highspin state for the studied FeII complexes (including FeP(Im), a model of the active site of myoglobin). A larger overstabilization of the highspin states was observed for the M06 and M06L functionals, up to 22 and 11 kcal/mol, respectively. None of the tested density functionals consistently provides a better accuracy than CASPT2 for all model complexes.  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the electronic structure (ground and excited states) and g matrix of a model compound for oxomolybdenum enzymes featuring the MoO–dithiolate moiety in C s symmetry, by means of multiconfigurational secondorder perturbation theory (CASPT2) for a range of fold angles (5–29°), i.e. the angle between the S–Mo–S and S–C–C–S planes of the dithiolate ligand. We found no evidence of a suggested 3center pseudoσ bonding interaction between the singly occupied orbital of the ground state and the symmetric inplane dithiolate orbital (Inscore et al. in Inorg Chem 38:1401–1410, 1999). This is complemented with our alternative assignment of band 4 in the electronic spectrum as the transition out of the a″ instead of the a′ dithiolate inplane orbital into the singly occupied groundstate orbital, believed to probe the dominant hole superexchange pathway (Inscore et al. in Inorg Chem 38:1401–1410, 1999; Burgmayer et al. in J Inorg Biochem 101:1601–1616, 2007). Principal g values of 1.9652, 1.9090, 2.0003 were obtained at a fold angle of 21°. The latter value is so close to the free electron g e factor is due to an important positive contribution from the LMCT transition corresponding to band 4, counteracting the negative contributions from the ligand field transitions.  [Show abstract] [Hide abstract]
ABSTRACT: The structural, electronic and magnetic properties of two different models of the heterospin polymer chain complexes of Cu2+ hexafluoroacetylacetonate with two pyrazolesubstituted nitronyl nitroxides Cu(hfac)2L(R) have been studied by means of multiconfigurational perturbation theory based on a CASSCF (complete active space selfconsistent field) wave function, i.e. the CASPT2 method. Our calculations reveal the presence of two minima in the electronic energy curve along the CuO(L) bond, separated by only 6 kcal/mol, and corresponding to the Xray structures of the CuO6 centers in Cu(hfac)2L(Pr) at 115 and 293 K, respectively. The two energetic minima are characterized by a different electronic structure, thus giving rise to a different threespin exchange coupling and explaining the thermally induced spin transitions in this family of compounds. The concomitant variations in the magnetic properties, i.e. g factors and magnetic moments mu(eff)(T) were calculated and compared with the experimental data of Cu(hfac)2L(Pr). Even if the correspondence is only qualitative, our calculations provide a convincing explanation of the observed magnetic peculiarities. In particular, at low temperatures, the predicted groundstate is 2A(u), well separated from the 2A(g), 4A(u) states and therefore exclusively populated. Its calculated g factors, g(parallel) = 1.848, g(perpendicular) = 1.965, 1.974, qualitatively correspond to the observed g < 2 signals in the lowtemperature EPR spectra. The previously assumed formal spin assignment >NO*Cu*ON < for these linear spin triads is challenged by our calculations, pointing instead to a more important role of the endstanding NO in the exchange interactions with Cu(II).  [Show abstract] [Hide abstract]
ABSTRACT: Calculations of the g tensor of three copper(II) complexes [Cu(NH3)4]2+, [CuCl4]2, and plastocyanin are presented. Two different sumoverstatesbased approaches are considered, making use of the multistate CASPT2 method for excitation energies and PMCAS (perturbation modified CAS) wave functions for the computation of the angular momentum and spinorbit coupling matrix elements. Test calculations on [Cu(NH3)4]2+ and [CuCl4]2 point to the need of including in the MSCASPT2 treatment the specific chargetransfer state with an electron excited out of the bonding counterpart of the groundstate SOMO. The computed g shifts for these two molecules present a considerable improvement with respect to the results obtained from our previous g tensor calculations based instead on CASSCF/CASPT2. This is shown to be related to an improved description of the covalency of the CuL bonds. For the calculations on plastocyanin, different models are used, taken from a recent (QM/MM) DFT study by Sinnecker and Neese. The effect of the surrounding protein is taken into account by surrounding the central cluster either with a dielectric continuum (epsilon = 4) or with a set of point charges. The second approach is found to be indispensable for an accurate description of environmental effects. With this approach, the calculated g values compare to within 30 ppt with the experimental data of plastocyanin.  [Show abstract] [Hide abstract]
ABSTRACT: Highlevel ab initio calculations using multiconfigurational perturbation theory [complete active space with secondorder perturbation theory (CASPT2)] were performed on the transition energy between the lowest highspin (corresponding to (5T2g) in Oh) and lowspin (corresponding to 1A1g in Oh) states in the series of sixcoordinated Fe(II) molecules [Fe(L)(NHS4)], where NHS4 is 2,2'bis(2mercaptophenylthio)diethylamine dianion and L=NH3, N2H4, PMe3, CO, and NO+. The results are compared to (previous and presently obtained) results from density functional theory (DFT) calculations with four functionals, which were already shown previously by Casida and coworkers [Fouqueau et al., J. Chem. Phys. 120, 9473 (2004); Ganzenmuller et al., ibid. 122, 234321 (2005); Fouqueau et al., ibid. 122, 044110 (2005); Lawson Daku et al., ChemPhysChem 6, 1393 (2005)] to perform well for the spinpairing problem in these and other Fe(II) complexes, i.e., OLYP, PBE0, B3LYP, and B3LYP*. Very extended basis sets were used both for the DFT and CASPT2 calculations and were shown to be necessary to obtain quantitative results with both types of method. This work presents a sequel to a previous DFT/CASPT2 study of the same property in the complexes [Fe(H2O)6]2+, [Fe(NH3)6]2+, and [Fe(bpy)3]2+ [Pierloot et al., J. Chem. Phys. 125, 124303 (2006)]. The latter work was extended with new results obtained with larger basis sets and including the OLYP functional. For all considered complexes, the CASPT2 method predicts the correct ground state spin multiplicity. Since experimental data for the actual quintetsinglet (free) energy differences are not available, the performance of the different DFT functionals was judged based on the comparison between the DFT and CASPT2 results. From this, it was concluded that the generalized gradient OLYP functional performs remarkably well for the present series of ferrous compounds, whereas the success of the three hybrid functionals varies from case to case.  [Show abstract] [Hide abstract]
ABSTRACT: The computation of the electronic g tensor by two multireference methods is presented and applied to a selection of molecules including CN, BO, AlO, GaO, InO, ZnH, ZnF, O(2), H(2)O(+), O(3) (), and H(2)CO(+) (group A) as well as TiF(3), CuCl(4) (2), Cu(NH(3))(4) (2+), and a series of d(1)MOX(4) (n) compounds, with M=V, Cr, Mo, Tc, W, Re and X=F, Cl, Br (group B). Two approaches are considered, namely, one in which spinorbit coupling and the Zeeman effect are included using secondorder perturbation theory and another one in which the Zeeman effect is added through firstorder degenerate perturbation theory within the groundstate Kramers doublet. The two methods have been implemented into the MOLCAS quantum chemistry software package. The results obtained for the molecules in group A are in good agreement with experiment and with previously reported calculated g values. The results for the molecules in group B vary. While the g values for the d(1) systems are superior to previous theoretical results, those obtained for the d(9) systems are too large compared to the experimental values.
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514  Citations  
84.36  Total Impact Points  
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Institutions

2015

Lund University
Lund, Skåne, Sweden


20062014

University of Leuven
 • Department of Chemistry
 • Institute of Nanoscale Physics and Chemistry (INPAC)
Louvain, Flanders, Belgium


2011

Catholic University of Louvain
 School of Chemistry
ЛувенлаНев, Walloon, Belgium
