The Parameterization And Application Of The Polarization Force Field Of Organic Conjugated Small Molecules AMOEBA

Organic conjugated molecular systems and their derivatives play an important role in organic semiconductor materials and also have attracted widespread attention.One of the important indicators to measure the performance of organic semiconductor materials is the charge transfer rate.The higher the charge transfer rate,the better the conductivity,so the factors affecting the charge transfer rate become the focus of this paper.In this paper,we have chosen the azabenzenes homodimers and acene crystals as our research object,using the AMOEBA polarizable force field,first under the premise of the standard van der Waals dispersion parameter and the default atomic polarizability of the polarizable force field.The electrostatic potential is obtained by fitting the multipole parameter of different density functionals,and the intermolecular interaction energy of the nitrogen-containing heterocycle is obtained,then the polarizability of the paraphenylene intermolecular parameters is re-fitted using the QTAIM method.The external reorganization energy of acenes was also evaluated based on the standard van der Waals dispersion parameter of the polarizable force field.The details are as follows:Chapter one:The classification of organic semiconductor charge transport materials is briefly introduced,Organic conjugated molecular systems play an important role in organic semiconductor charge transport materials due to their own characteristics.At the same time,several major steps of the charge transfer process are introduced.Summarize several factors that affect charge transfer rate,such as charge transfer integral,reorganization energy,molecular stacking,and temperature.Chapter two:The development and the basic principles of the quantum chemistry,density functional theory and AMOEBA polarizable force field are briefly described.The advantages and disadvantages of the first-principles and force field calculation methods are briefly outlined.Because of the high computational cost,it is impractical to deal with some of the properties of large systems through first-principles.Traditional force fields often use the fixed atom point charges(APCs)to describe electrostatic interactions.These atom point charges(APCs)can be obtained by fitting QM calculated electrostatic potential(ESP)on some specific molecular surfaces.However,due to the isotropic nature of the point charges,the calculation of rigid ?-conjugated planar molecules is very challenging.In addition,due to the use of a fixed electrostatic model,these force fields lack the ability to respond to environmental charges.Therefore,the use of atom multipole(AMP)makes AMOEBA polarizable force field a good description of electrostatic potential,while the default Thole atomic polarizability also responds well to electron polarization.Based on the above reasons,the AMOEBA polarizable force field has become our preferred method.Chapter three:Based on the organic conjugated molecular system,we first selected the azabenzenes homodimers as our research object,using the AMOEBA polarizable force field based on different density functional methods,the atom multipole parameter of the azabenzenes homodimers obtained by GDMA,under the premise of using the standard van der Waals dispersion parameter and the default atomic polarizability of the AMOEBA polarizable force field,the intermolecular interaction energy obtained compared with the standard value CCSD(T)/CBS intermolecular interaction.We find that the root-mean-square errors of all density functionals are less than?1.0 kcal/mol.In all selected density functionals,the functionals M11 and LC-VV10 are two optional functionalities for generating atom multipoles.The electrostatic potentials fitted based on these two methods are closer to the electrostatic potential of the MP2 method,even better.Next,we analyzed the electrostatic potentials of azabenzenes homodimers in four different conformations.It was found that in the four selected systems,electrostatic potential energy dominates the total intermolecular interaction energy.The proportion of polarization energy and van der Waals interaction energy will change with the conformation of the dimer.Chapter four:We selected the acene crystals as our another research object.Using the AMOEBA polarizable force field,we used the QTAIM method to refit the atom polarizability of the acene crystals intermolecular parameters.The polarizability of C and H atoms is not only fixed at a fixed value,but changes with the environment in which they are located.The van der Waals parameter still uses the AMOEBA force field default value,and the electrostatic potential parameter is based on the B3LYP/6-31G*horizontal fitted atom multipole.First of all,the total recombination energys of the acene crystals are obtained through the force field,then the internal reorganization energys of the acene crystals are obtained by the four-point model,at last the external recombination energys of the acene crystals are obtained by the total recombination energys subtracts the internal reorganization energys.We used QM method to evaluate the internal and external recombination energies of acene crystals obtained from AMOEBA polarizable force field,and the rationality of the AMOEBA polarizable force field was verified.In the study,we find that when the conjugate length is fixed,the external recombination energy of acene crystals will increase with the increase of the charge transfer distance.When the charge transfer distance is constant,the external recombination does not show a clear trend with the increase of the conjugation length,but internal restructuring can show a decreasing trend.