38 KB130 KB34 KB199820252011Daemen, LukeEckert, JürgenHartl, MonikaStare, Jernejštevilka:3letnik:58str. 521-527ISSN:1318-0207COBISSID:4834842URN:URN:NBN:SI:doc-WGQAPJ2QenSlovenian Chemical SocietySlovensko kemijsko društvoActa chimica slovenicaanalizna kemijaharmonic analysisinelasting neutron scatteringkvantna dinamikamolekulska dinamikaneelastična nevronska vibracijska spektroskopijaperiodic DFT calculationsshort hydrogen bondingvibrational dynamicsvodikova vezThe very short hydrogen bond in the pyridine N-oxide - trichloroacetic acid complex: an inelastic neutron scattering and computational study|We have investigated the dynamics of the very short hydrogen bond (RO...O = 2.430 A) of the pyridine N-oxide trichloroacetic acid complex in the solid state by combining vibrational spectroscopy using inelastic neutron scattering with extensive computational studies and analysis of the vibrational spectra. The Density Functional Theory (DFT) computational models used ranged from the isolated gas phase cluster to three approaches with periodic boundary conditions, namely CRYSTAL, CPMD and VASP, all of which, however calculate frequencies in the harmonic approximation. While all but the gas phase calculation yield structural parameters for the hydrogen bond in reasonable agreement with experiment, only the periodic VASP and CPMD approaches resulted in INS spectra (calculated with the program a-climax) that adequately reproduced some of the key features of the experimental spectrum related to the in-plane and outof-plane bending modes of the H-bond. No clear indication was found either in experiment or computational studies for OH stretching. More sophisticated and time-consuming calculations are therefore indicated to elaborate on the hydrogen bond dynamics including molecular dynamics simulations or the use of quantum dynamics on multidimensional potential energy surfacesZ metodo neelastične nevtronske vibracijske spektroskopije (INS) ter računskimi metodami smo proučevali dinamiko kratke vodikove vezi (ROO = 2.430 A) v kompleksu piridin N-oksida in triklorocetne kisline v trdnem kristaliničnem stanju. Uporabili smo računske metode, ki temeljijo na teoriji gostotnih funkcionalov, in sistem obravnavali na več nivojih (glede na kompleksnost okolice), od izoliranega kompleksa do polnega periodičnega modela. Uporabili smo tri programe za periodično modeliranje (CRYSTAL, CPMD in VASP) ter z njimi izračunali vibracijske frekvence v harmonskem približku; INS spektre smo izračunali na podlagi harmonskih frekvenc z uporabo programa a-cilmax. Medtem ko vsi modeli z izjemo izoliranega dobro opišejo strukturo kompleksa, pa je ujemanje izračunanega spektra z izmerjenim (v delih, povezanih z upogibnimi nihanji protona v vodikovi vezi) zadovoljivo le pri programih CPMD in VASP. V izmerjenem spektru prispevek valenčnega nihanja protona ni opazen, račun pa kaže, da je njegova intenziteta zelo nizka. Za primerno računsko obravnavo dinamike vodikove vezi v tem sistemu je nujna uporaba bolj zahtevnih tehnik, kot so metode molekulske dinamike ter kvantne dinamike na multidimenzionalni potencialni ploskviTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaSlovensko kemijsko društvo