《分子电子结构》研究生课程教学资源（Electronic Structure of Molecules）ESM-4-triplet-freq

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

Imaginary frequencyIn Log file: Normal termination+②freq, optimizedstructure has no imaginary frequencyFull mass-weighted force constant matrix:freguencies ---0.00100.00030.000411.215918.846023.1154Low252.7405303.0365418.4182LowfreguenciesDiagonal vibrational polarizability:4.58704331.389586942.9926634frequencies (cm*-l), IR intensitiesHarmonic(KM/Mole)，Raman scatteringe.g. of imaginary frequencyFullmass-weighted forceconstant matrix:0.0025-50.5973-10.1954-0.00080.0026Lowfreguencies-11.7144fregLowEreguencies (negative signs)imaginaryHarmonic(KM/Mole)Raman scatteringLreguenciesIRintensitiesm

In Log file: ①Normal termination+②freq, optimized structure has no imaginary frequency e.g. of imaginary frequency: Imaginary frequency

ThemochemistryThemochemistry data, find “enthalpyzero-pointcorrection=0.080324(Hartree/Particle)0.084586Thermal correction to Energy=0.085530Thermal correction toEnthalpy0.054960Thermal correction to Gibbs Free Energy=-154.953482sum of electronic and zero-point Energies=-154.949219Sumof electronic andthermal Energies=-154.948275Sum of electronic and thermal Enthalpies-154.978845Sumof electronic and thermal Free Energies-

Themochemistry data, find “enthalpy” Themochemistry

Normal modesXLog file( or out file):G1:M1:V1-DisplayVibrations口Results-VibrationsMode#FreqInfrared32.04121252.732303.0399.03003418.4211.29624831.070.01615912.1510.142261043.2956.201771124.2722.887381195.174.883991292.8286.6220100.07821310.94Animate VibrationStart AnimationSave Movie.Animation Frequency:Displacement Amplitude:Soale:Show Displacement VectorsScale:Show Dipole Derivative Unit VectorManual Displacement:0.00Seye Struoture.CloseCancelHelpSpectrum

Log file( or out file): Results -Vibrations Normal modes

IRspectraSpectrum口XG1:M1:V1-Vibrational SpectraPlotsIR Spectrum3501400D (10-40 esu2 cm2)12003001000250s800200-6001504001002005000TUTUTTTTTTTTTTTTTTTTTTTTTTTTTTT05001500200025003000100035004000(cm-1)FrequencyFrequency(cm)=252.726,D(10-40esu?cm)=505.786Right clickproperties-invert axis

Right click—properties—invert axis IR spectra

Freguency calibrationfactorDuring freq calc. add keyword scale=X (X is the factor), e.g.# HF/6-31g(d) freq scale=0.8953Scale onlyaffectsthethermochemistry(energy corrections)and doesnot affect the vibrational frequency in log file or in GV's vibration.Frequencies has to be manually changed by timing the correctionfactor.Example,ethanolfreq.calc.withfreq.correction#optfreqb3lyp/6-31g(d)scale=0.9614Thermochemistrydata:Zero-point correction=0.077223(Hartree/ParticleThermal correction to Energy0.081570Thermal correction toEnthalpy0:082514Thermal correction toGibbs Free Energy-0.051802Sum of electronic and zero-point Energies-154.956582-154.952235Sum of electronicthermalEnergies-andSum of electronicEnthalpies=-154.951291andthermal-154.982003sum ofelectronicandthermalFreeEnergies-

During freq calc. add keyword scale=X (X is the factor), e.g. # HF/6-31g(d) freq scale=0.8953 Scale only affects the thermochemistry (energy corrections) and does not affect the vibrational frequency in log file or in GV’s vibration. Frequencies has to be manually changed by timing the correction factor. Example, ethanol freq. calc. with freq. correction # opt freq b3lyp/6-31g(d) scale=0.9614 Thermochemistry data: Frequency calibration factor