OptimizationIfMO,NBOandWibergbondorderaretoNH2H2Ncomputed, how would you do it?Opt + SP (need to use the same model chemistry?)Using different methods or basis sets, will the optimizedstructures/totalenergies/energydifferencebetweenisomersbedifferent?openepoxideisomerisomerForesman,exercise3.2
Optimization If MO, NBO and Wiberg bond order are to be computed, how would you do it? Using different methods or basis sets, will the optimized structures/total energies/energy difference between isomers be different? Opt + SP (need to use the same model chemistry?) Foresman, exercise 3.2
OptimizationBiggermoleculesG2:M1:V1 -Gaussian Calculation SetupTitle:Keywords:#hf/3-2lggeom=connectivityCharge/Mult.:01MethodTitlePBCJob TypeLinkoGeneralGuessPop.Hartree-FockDefault SpinMethod:Ground StateMechanics3-21GBasisSet:Semi-empiricalHartree-Fock0ACharge:Spin:DFT.MP2MP4CCSDBDCASSCFompoundICustom
Optimization Bigger molecules
Bondorder2.Build themolecules below. calculate their Wibergbond order, compare their MOs and NBOs,using the model chemistry of hf/3-21gocta-1.3.5.7-tetraeneKeyword:pop=nboreadAdditional input: snbo bndidx sendBy default,MO (Lewis)bond orderiscalculated;Wiberg (NBO) bond order will be computedfor thefirst and last optimization step;
2.Build the molecules below, calculate their W iberg bond order, compare their MOs and NBOs, using the model chemistry of hf/3-21g. Bond order octa-1,3,5,7-tetraene Keyword: pop=nboread Additional input: $nbo bndidx $end • By default, MO (Lewis) bond order is calculated; • Wiberg (NBO) bond order will be computed for the first and last optimization step;
Singlet vs. tripletC atom: 1s?2s?2p2, need optimization?calculation setup/method/custom/ m062x/6-31+G(d)O,: singlet vs triplet, opt using the model chemistryof APFD/6-311+G(2d)Molecular OrbitalMolecular OrbitaloOxygenOxygenOxygenOxygen11111中32g 0, triplet14,02 singletDiamagnetic Paramagnetic1st excited state, E higher by 1 eVGroundstateLifetime1sto45mindO-O 1.2074 A·dO-0O 1.2155 ADifferent reactivity,followingDiradical following radicaldouble bond
Singlet vs. triplet C atom: 1s22s22p2 , need optimization? calculation setup/method/custom/ m062x/6-31+G(d) O2 : singlet vs triplet, opt using the model chemistry of APFD/6-311+G(2d) • 1∆g O2 singlet • Diamagnetic • 1 st excited state, E higher by 1 eV • Lifetime 1s to 45 min • dO-O 1.2155 Å • Different reactivity, following double bond • 3Σg - O2 triplet • Paramagnetic • Ground state • dO-O 1.2074 Å • Diradical following radical
Freguency calculationKeyword: freq is used after geometry optimization, but the model chemistrymust bethe sameas the one usedforoptimization!Opt and freq can be done together (keyword:opt+freg) actually two sequeljobs;By default, output contains: vibration frequencies, polarizability, IR intensity,thermochemistrydata,etc.Frequency calc. of ethanol1.#freqb3lyp/6-31g(d)Use Gaussview to open the normal terminated log file (or chk file),Calculate-Gaussian calculation setup to set the new freg.calc.job;2. #opt freqjb3lyp/6-31g(d)UseGaussviewtobuilda ethanol,inCalculate-Gaussiancalculation setup, set opt+freq job
# freq b3lyp/6-31g(d) Keyword: freq is used after geometry optimization, but the model chemistry must be the same as the one used for optimization! Opt and freq can be done together (keyword: opt+freq) actually two sequel jobs; By default, output contains: vibration frequencies, polarizability, IR intensity, thermochemistry data, etc. # opt freq b3lyp/6-31g(d) Use Gaussview to open the normal terminated log file (or chk file), Calculate-Gaussian calculation setup to set the new freq. calc. job; Use Gaussview to build a ethanol, in Calculate-Gaussian calculation setup, set opt+freq job。 Frequency calculation Frequency calc. of ethanol 1. 2