Calculation Of Molecular Total Energies Of Several Organic Systems And Oligopeptide In Terms Of ABEEMσπ/MM Method

Molecular total energies of naphthene Cn2n (n=6～12), alcohol GnH2n-1OH (n=1～8), aldehyde CnH2nO (n=1～8) and acid CnH2n-1COOH (n=0～8) were calculated in terms of ABEEMσπMM method. Compared with the molecular total energies calculated by ab initio (MP2/6-311+G(d,p) method, the minimum absolute deviation is0.0000kal/mol, the maximal absolute deviation is9.0601kal/mol; the minimum relative deviation is0.0000, the maximal relative deviation is3.1134×10-5; the RMSD of naphthene, alcohol, aldehyde and acid are1.3068kal/mol,1.8952kal/mol,2.3504kal/mol and3.1269kal/mol, respectively, and their relative RMSD are0.3211×10-5,0.5650×10-5,0.7769×10-5and0.7715×10-5, respectively; the linear correlation coefficients of the energies calculated by the two methods are all1.0000. So it’s quite accurate to calculate molecular energies by ABEEMσπMM method. Applying this method to large systems (dipeptide to octapeptide of glycine, alanine, serine and leucine), we calculated these molecular energies under the conformations of antiparallel β-pleated sheet and α-right hand helix. Compared with the energies calculated by ab initio (MP2/6-311++G(d,p) method, the absolute deviation is less than1.7893kcal/mol, the relative deviation is0.4828×10-5under the conformations of antiparalle β-pleated sheet; the RMSD and relative RMSD are1.0554kcal/mol and0.1170×10-5, respectively; the linear correlation coefficients are all1.0000. The absolute deviation is less than5.1523kcal/mol, the relative deviation is0.6016×10-5under the conformations of α-right hand helix; the RMSD and relative RMSD are2.6671kcal/mol and0.1695×10-5, respectively; the linear correlation coefficients are all1.0000. The results show that molecular total energies can be calculated quickly and accurately by ABEEMσπ/MM method, the advantages of fast speed is more obvious especially for large systems, and the parameters have good transferability at the same time. So, ABEEMσπ/MM method is a reliable and developmental method to calculate molecular total energies quickly and accurately.