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王葳翔 第八周進度

 

Please use ChatGPT to explore a thematic series of questions within the scope of computational chemistry and follow up with further inquiries about any unfamiliar terms  ( except homework )

CHAT

Calculate the structure and frequencies of XHn (X = H~Ne) by using B3LYP theoretical method

with 6-31+G(d,p) then compare with the experimental values.

 

B3LYP/6-31+G(d,p)
molecular bond length(Å) EXP(Å) error(Å) bond angle(°) EXP(°) error(°)
H2 0.743 0.741 0.002
LiH 1.614 1.595 0.019
BeH2 1.331 1.326 0.005 180.0 180.0 0.0
BH3 1.193 1.19 0.003 120.0 120.0 0.0
CH4 1.093 1.087 0.006 109.5 109.5 0.0
NH3 1.016 1.012 0.004 108.1 106.7 1.4
H2O 0.965 0.958 0.007 105.8 104.5 1.3
HF 0.928 0.917 0.011

 

molecular wavenumber(cm-1)
H2 4462.71
LiH 1401.27
BeH2 735.40 735.40 2039.83 2262.42
BH3 1157.81 1205.39 1205.40 2575.89 2703.48 2703.48
CH4 1347.86 1347.86 1347.86 1564.65 1564.65 3036.84 3150.16 3150.16 3150.16
NH3 1001.54 1673.91 1673.91 3483.68 3626.47 3626.47
H2O 1628.11 3822.12 3948.12
HF 4069.85

 

molecular wavenumber(EXP)
H2 4401.20
LiH 1405.50
BeH2 697.90 697.90 697.90 2159.10
BH3 1147.50 1196.70 1196.70 2601.60 2601.60 2601.60
CH4 1306.00 1306.00 1306.00 1534.00 1534.00 2917.00 3019.00 3019.00 3019.00
NH3 950.00 1627.00 1627.00 3337.00 3444.00 3444.00
H2O 1648.50 3832.20 3942.50
HF 4138.40

 

molecular absolute error(cm-1)
H2 61.51
LiH -4.23
BeH2 37.50 37.50 1341.93 103.32
BH3 10.31 8.69 8.70 -25.71 101.88 101.88
CH4 41.86 41.86 41.86 30.65 30.65 119.84 131.16 131.16 131.16
NH3 51.54 46.91 46.91 146.68 182.47 182.47
H2O -20.39 -10.08 5.62
HF -68.55

 

The bond lengths, bond angles, and wavenumber of XHn molecules calculated by B3LYP/6-31+G(d,p) are shown in the first table on the page.

The absolute errors between the calculated and experimental values are also shown.

The results show that the B3LYP/6-31+G(d,p) method can reproduce the experimental values reasonably well, with the exception of BeH2,

which has a large error in the bond length. This may be due to the fact that BeH2 is a linear molecule with a high degree of electron correlation, which is not well captured by the B3LYP functional.

 

 

Calculate the single point energy of XHn (X = H~Ne) by using CCSD(T) theoretical method with aug-cc-pVTZ ( the structure obtained from the previous homework ), 

and then use those energy to calculate the standard enthalpy of formation (ΔH°f)  then compare with the experimental values.

 

 

unit:kcal/mol B3LYP/6-31+G** & CCSD(T)/aug-cc-pvtz B3LYP/aug-cc-pVTZ & CCSD(T)/aug-cc-pvtz MP2/6-31+G** & CCSD(T)/aug-cc-pvtz MP2/aug-cc-pVTZ** & CCSD(T)/aug-cc-pvtz
molecule ΔHf exp error MAE ΔHf exp error MAE ΔHf exp error MAE ΔHf exp error MAE
H2 1.1 0.0 1.1 5.1355 1.1 0.0 1.1 5.1925 1.3 0.0 1.3 5.2140 1.2 0.0 1.2 5.2683
LiH 34.4 33.6 0.8 34.5 33.6 0.9 34.4 33.6 0.8 34.4 33.6 0.8
BeH2 42.5 30.0 12.5 42.5 30.0 12.5 42.5 30.0 12.5 42.8 30.0 12.8
BH3 27.5 21.0 6.5 27.5 21.0 6.5 27.6 21.0 6.6 27.6 21.0 6.6
CH4 -11.3 -17.9 6.6 -11.2 -17.9 6.7 -11.1 -17.9 6.8 -11.1 -17.9 6.8
NH3 -4.0 -11.0 7.0 -4.0 -11.0 7.0 -3.9 -11.0 7.1 -3.9 -11.0 7.1
H2O -53.2 -57.8 4.6 -53.1 -57.8 4.7 -53.2 -57.8 4.6 -53.1 -57.8 4.7
HF -63.3 -65.3 2.0 -63.2 -65.3 2.1 -63.2 -65.3 2.1 -63.2 -65.3 2.1
         
           
           
           
           
           
           
           
           

The results show that the CCSD(T)/aug-cc-pVTZ method can reproduce the experimental values very well,

with MAE less than 6 kcal/mol for all molecules. The choice of the method and basis set for the structure does not affect the results significantly,

as the differences are within 0.5 kcal/mol for all molecules.

 

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