An effective exciton Hamiltonian for all amide bands is used to calculate the linear absorption and photon echo spectra of a 17 residue helical peptide (YKKKH17). The cross peak bandshapes are sensitive to the inter-band couplings. Fluctuations of the local amide frequencies of the all amide fundamental and their overtone and combination states are calculated using the multipole electric field induced by environment employing the electrostatic DFT map of N-methyl acetamide. Couplings between neighboring peptide units are obtained using the anharmonic vibrational Hamiltonian of glycine dipeptide (GLDP) at the BPW91/6-31G(d,p) level. Electrostatic couplings between non-neighboring units are calculated by the fourth rank transition multipole coupling (TMC) expansion including 1/R3 (dipole-dipole), 1/R4 (quadrupole-dipole), and 1/R5 (quadrupole-quadrupole and octapole-dipole) interactions.
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机译：所有酰胺带的有效激子哈密顿量用于计算17个残基螺旋肽（YKKKH17）的线性吸收和光子回波谱。交叉峰的带形对带间耦合敏感。使用N-甲基乙酰胺的静电DFT图，利用环境诱导的多极电场，计算所有酰胺基态及其泛音和组合态的局部酰胺频率的波动。使用甘氨酸二肽的非谐振动哈密顿量（GLDP）在BPW91 / 6-31G（d，p）水平获得相邻肽单元之间的偶联。非相邻单元之间的静电耦合是通过四阶跃迁多极耦合（TMC）展开来计算的，其中包括1 / R 3 （偶极-偶极子），1 / R 4 （四极-偶极）和1 / R 5 （四极-四极和八极-偶极）相互作用。
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