TATB基PBX结合能和力学性能的理论研究

以SCF-MO-AM1方法和MM-COMPASS力场, 对TATB (1,3,5-三氨基-2,4,6-三硝基苯)与系列高聚物组成的PBX(高聚物粘结炸药)尺寸匹配原子簇, 分别进行全优化几何构型计算, 发现两种方法求得的结合能存在良好的线性关系. 对TATB (3×3×4)超晶胞及其与系列氟聚物组成的双组分PBX, 实施COMPASS力场下的分子动力学(MD)周期性模拟计算, 首次求得其弹性系数、模量和泊松比, 发现添加少量高聚物即能有效改善炸药的力学性能.     

分子动力学模拟浓度和温度对TATB/PCTFE PBX力学性能的影响

为探讨高聚物粘结炸药(Polymer Bonded Explosive, PBX)的力学性能随温度和高聚物浓度而变化的规律, 用分子动力学(MD)方法和compass力场, 对著名高能炸药1,3,5-三氨基-2,4,6-三硝基苯(TATB)与常用高聚物粘结剂聚三氟氯乙烯(PCTFE)所构成的TATB/PCTFE PBX进行模拟计算. 结果表明, 在一定范围内, 随高聚物浓度的增加, PBX的弹性系数和模量减小, 表明其刚性减小、弹性增加; 而随温度的升高, PBX的刚性减小、弹性增强. 还发现PBX的结合能随浓度增高而增大, 随温度升高而减小.     

HMX/F2311 NPT高聚物粘合炸药力学性能的NPT系综分子动力学模拟研究

本文用分子动力学模拟方法研究了以β型奥克托金(β-HMX)含能材料为基,以氟聚物F2311为粘合剂的高聚物粘合炸药(PBX)的力学性能。β-HMX晶体和以其为基的高聚物粘合炸药的弹性常数均由静态弹性常数分析法计算求得，而工程模量和泊松比则由Reuss平均法导出。根据柯西压和本体模量与剪切模量的比值，发现通过加入少量该种聚合物可有效地提高HMX晶体的延展性。     

ε-CL-20基PBX结构和性能的分子动力学模拟——HEDM理论配方设计初探

以高能量密度化合物ε-CL-20(六硝基六氮杂异伍兹烷)为主体,分别添加5种高聚物黏结剂(Estane5703、GAP、HTPB、PEG和F2314)构成高聚物黏结炸药(PBXs).用分子动力学(MD)方法模拟研究各PBX的结合能、相容性、安全性、力学性能和能量性质,通过比较和分析,为优选黏结剂、指导HEDMs配方设计提供信息和规律.由结合能预测各PBX的相容性和稳定性排序为:ε-CL-20/PEG>ε-CL-20/Estane5703≈ε-CL-20/GAP>ε-CL-20/HTPB>ε-CL-20/F2314.以对相关函数g(r)描述了组分之间相互作用的方式.5种黏结剂的少量加入均能显著改善ε-CL-20的弹性力学性能,增强各向同性.各黏结剂并非通过改变ε-CL-20的分子结构影响PBX的感度.它们主要通过自身的热容(C°p)和密度(ρ)影响PBX的安全性和能量性质.     

HTPB与Al不同晶面结合能和力学性能的分子动力学模拟

采用分子力学(MM)和分子动力学(MD)方法, 在250、300、350、400、450 K, 对固体推进剂端羟基聚丁二烯(HTPB)和铝晶胞不同晶面结构所组成的层模型在COMPASS力场下, 进行模拟计算, 求得结合能和静态力学性能(弹性系数、模量和泊松比). 模拟结果表明, 在400 K时HTPB与Al(011)面的结合能最大, 从综合力学性能优劣上看, 各个面从优到劣的排序为(011)>(221)>(001), HTPB与Al的结合能与力学性能具有对应关系, 结合能大的力学性能优异, 结合能小的力学性能较差.     

CL-20/HMX共晶及其为基PBX界面作用和力学性能的MD模拟研究

为提高共晶炸药的实际使用价值, 改善其安全性和力学性能, 以CL-20/HMX共晶炸药为基, 分别添加2种高聚物粘结剂Estane 5703(聚氨基甲酸乙酯)和HTPB(端羟基聚丁二烯), 共构建两种共晶基高聚物粘结炸药(PBX)模型, 进行细致的295 K NPT分子动力学(MD)模拟研究. 通过两种PBX模型及其与该共晶炸药的MD模拟结果比较表明, 与基炸药之间的结合能Estane 5703大于HTPB, 预示含少量Estane 5703的PBX稳定性和相容性更佳; 对相关函数g(r)揭示粘结剂与基炸药界面相互作用的方式, 以基炸药中H分别与Estane 5703中羰基O和HTPB中端羟基O之间的氢键较强. 与CL-20/HMX共晶炸药相比, 少量粘结剂Estane 5703或HTPB的加入, 使弹性系数C_ij下降, 拉伸模量(E)、体积模量(K)和剪切模量(G)均显著减小, 而泊松比(ν), 柯西压(C₁₂－C₄₄)和K/G值明显增大, 表明PBXs体系刚性减小, 延展性增强, 力学性能大为改善. 少量粘结剂包覆使PBXs致钝, 主要归因于其隔热、吸热并使体系变“软”的缓冲作用, 而界面作用造成的分子结构引发键键长变化变为次要因素.     

HMX和HMX/HTPB PBX的晶体缺陷理论研究

建立空位和掺杂点缺陷模型, 用分子动力学(MD)方法, 研究晶体缺陷对β-环四亚甲基硝胺(HMX)和β-HMX/HTPB(端羟基聚丁二烯)高聚物粘结炸药(PBX)的力学性能和爆炸性能的影响. 结果表明, 相对于HMX“完美”晶体(1)考察缺陷晶体(2和3), 以及相对于HMX完美晶体基PBX(1)考察缺陷PBX 2和PBX 3, 均发现弹性系数和(拉伸、体积、剪切)模量下降, 导致体系刚性减弱, 延展性和韧性增强. 这与在基炸药HMX晶体(1, 2和3)中分别加入HTPB高聚物粘结剂形成PBX 1, PBX 2和PBX 3呈现类似的相应的变化趋势和效果. 此外, 研究表明, 爆炸性质也依赖于体系的组成和结构. 因加入的是低能高聚物, 故PBX(1), PBX(2)和PBX(3)的爆热、爆速和爆压均比相应的基炸药(1, 2和3)低, 即晶体(1)＞PBX(1), 晶体(2)＞PBX(2), 晶体(3)＞PBX(3). PBX(1), PBX(2), PBX(3)与对应基炸药(1, 2, 3)的爆速和爆压取相同变化次序, 亦即PBX(1)＞PBX(2)＞PBX(3)对应于晶体(1)＞晶体(2)＞晶体(3). 这些计算结果和规律对PBX配方设计显然具有指导作用.     

硝酸酯增塑剂力学性能和界面相互作用的分子动力学模拟

运用分子动力学(MD)方法, 模拟研究了硝化甘油(NG)及其与硝化三乙二醇(TEGDN)组成的硝酸酯增塑剂的低温力学性能. 结果表明, NG/TEGDN混合体系较NG单组分体系的刚性减弱, 延展性和各向同性增强. 结合能计算和径向分布函数分析揭示了混合型硝酸酯增塑剂组分之间的相互作用及其本质.     

HTPB与A1不同晶面结合能和力学性能的分子动力学模拟

采用分子力学（MM）和分子动力学（MD）方法,在250、300、350、400、450K,对固体推进剂端羟基聚丁二烯（HTPB）和铝晶胞不同晶面结构所组成的层模型在COMPASS力场下,进行模拟计算,求得结合能和静态力学性能（弹性系数、模量和泊松比）．模拟结果表明,在400K时HTPB与A1（011）面的结合能最大,从综合力学性能优劣上看,各个面从优到劣的排序为（011）〉（221）〉（001）,HTPB与A1的结合能与力学性能具有对应关系,结合能大的力学性能优异,结合能小的力学性能较差．     

HMX/TATB复合材料弹性性能的MD模拟

用分子动力学(MD)方法COMPASS力场, 分别在正则系综(NVT)和等温等压系综(NPT)下, 模拟计算了著名常用高能炸药HMX(环四甲撑四硝胺)与著名钝感炸药TATB (1,3,5-三氨基-2,4,6三硝基苯)所构成的混合体系在室温时的弹性性能和结合能. 结果表明, 在NVT和NPT两种系综下模拟所得结果呈平行一致的趋势; 与纯HMX相比, HMX/TATB复合材料的拉伸模量、体模量和剪切模量均有所下降; 在NVT系综下, 还完成了HMX/TATB混合体系的不同温度的MD模拟. 发现当温度在245～345 K范围时, 体系的刚性和弹性变化很小; 但当温度达到395 K时, 材料的刚性减弱, 柔性增强.     

Molecular dynamics simulations for pure epsilon-CL-20 and epsilon-CL-20-based PBXs

Molecular dynamics has been employed to simulate the well-known high energy density compound epsilon-CL-20 (hexanitrohexaazaisowurtzitane) crystal and 12 epsilon-CL-20-based PBXs (polymer bonded explosives) with four kinds of typical fluorine polymers, i.e., polyvinylidenedifluoride, polychlorotrifluoroethylene, fluorine rubber (F(2311)), and fluorine resin (F(2314)) individually. The elastic coefficients, isotropic mechanical properties (tensile moduli, bulk moduli, shear moduli, and poission's ratios), and bonding energy are first reported for epsilon-CL-20 crystal and epsilon-CL-20-based polymer bonded explosives (PBXs). The mechanical properties of epsilon-CL-20 can be effectively improved by blending with a small amount of fluorine polymers, and the whole effect of the adding fluorine polymers to improve mechanical properties of PBXs along the three crystalline surfaces of epsilon-CL-20 is found to be (100) approximately (001) > (010). The interaction between each of the crystalline surfaces and each of the fluorine polymers is different, and the ordering of binding energy for the three surfaces is (001) > (100) > (010); F(2314) always has the strongest binding ability with the three different surfaces. F(2314) can best improve the ductibility and tenacity of PBX when it is positioned on epsilon-CL-20 (001) crystal surface. The calculations on detonation performances for pure epsilon-CL-20 crystal and the four epsilon-CL-20-based PBXs show that adding a small amount of fluorine polymer into pure epsilon-CL-20 will lower detonation performance, but each detonation parameter of the obtained PBXs is still excellent.     

TATB/氟聚物PBX力学性能、结合能和爆炸性能的模拟计算

Molecular dynamics （MD） method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene （TATB） coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.     

Molecular dynamics simulations of trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin-based polymer-bonded explosives

Molecular dynamics has been applied to investigate the low-sensitivity explosive TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin)-based polymer-bonded explosives (PBXs) with four typical fluorine polymers, PVDF (polyvinylidenedifluoride), PCTFE (polychlorotrifluoroethylene), F(2311) (fluorine rubber), and F(2314) (fluorine resin). The elastic constants, mechanical properties (tensile modulus, bulk modulus, shear modulus, and Poission ratio), binding energies, and detonation performances are first reported for the TNAD-based PBXs. The results show that the mechanical properties of TNAD can be effectively improved by the addition of small amounts of fluorine polymers, and the overall effect of fluorine polymers on the mechanical properties of the PBXs along three crystalline surfaces is (001) > (010) > (100). On each crystal surface, improvement in the ductibility made by the fluorine polymers changes approximately in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The binding energies between different TNAD crystalline surfaces and different polymer binders with the same chain segment or mass fraction both decrease in the order of (010) > (100) > (001). The binding properties of the polymers with the same chain segment on each crystal surface of TNAD increase as PVDF < F(2311) < F(2314) < PCTFE, while those of different polymers in the same content decrease in the sequence of PVDF > F(2311) > F(2314) > PCTFE. The detonation performances of the PBXs decrease in comparison with the pure crystal, but they are superior to those of TNT.     

Molecular dynamics simulation of mechanical properties of TATB/fluorine-polymer PBXs along different surfaces

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is the well-known high insensitive explosive. With TATB as the main body (90% and above) the polymer bonded explosives ( PBXs) contain a small amount of poly-mers (5%―10%). The composite materials with good saf…     

新型二氟甲基磷酸类酪氨酸蛋白磷酸酯酶1B抑制剂的分子动力学模拟和结合自由能计算

通过分子对接建立了一系列含二氟甲基磷酸基团(DFMP)或二氟甲基硫酸基团(DFMS)的抑制剂与酪氨酸蛋白磷酸酯酶1B(PTP1B)的相互作用模式, 并通过1 ns的分子动力学模拟和molecular mechanics/generalized Born surface area (MM/GBSA)方法计算了其结合自由能. 计算获得的结合自由能排序和抑制剂与靶酶间结合能力排序一致; 通过基于主方程的自由能计算方法, 获得了抑制剂与靶酶残基间相互作用的信息, 这些信息显示DFMP/DFMS基团的负电荷中心与PTP1B的221位精氨酸正电荷中心之间的静电相互作用强弱决定了此类抑制剂的活性, 进一步的分析还显示位于DFMP/DFMS基团中的氟原子或其他具有适当原子半径的氢键供体原子会增进此类抑制剂与PTP1B活性位点的结合能力.     

Molecular dynamics simulations on the structures and properties of ε-CL-20-based PBXs——Primary theoretical studies on HEDM formulation design

Five polymer bonded explosives (PBXs) with the base explosiveε-CL-20 (hexanitrohexaazaisowurtzitane), the most important high energy density compound (HEDC), and five polymer binders (Estane 5703, GAP, HTPB, PEG, and F2314) were constructed. Molecular dynamics (MD) method was employed to investigate their binding energies (Ebind), compatibility, safety, mechanical properties, and energetic properties. The information and rules were reported for choosing better binders and guiding formulation design of high energy density material (HEDM). According to the calculated binding energies, the ordering of compatibility and stability of the five PBXs was predicted as ε-CL-20/PEG ＞ ε-CL-20/ Estane5703 ≈ε-CL-20/GAP ＞ ε-CL-20/HTPB ＞ ε-CL-20/F2314. By pair correlation function g(r) analyses, hydrogen bonds and vdw are found to be the main interactions between the two components. The elasticity and isotropy of PBXs based ε-CL-20 can be obviously improved more than pure ε-CL-20 crystal. It is not by changing the molecular structures of ε-CL-20 for each binder to affect the sensitivity. The safety and energetic properties of these PBXs are mainly influenced by the thermal capability (C°p) and density (ρ) of binders, respectively.     

The generalized molecular fractionation with conjugate caps/molecular mechanics method for direct calculation of protein energy

A generalized molecular fractionation with conjugate caps/molecular mechanics (GMFCC/MM) scheme is developed for efficient linear-scaling quantum mechanical calculation of protein energy. In this GMFCC/MM scheme, the interaction energy between neighboring residues as well as between non-neighboring residues that are spatially in close contact are computed by quantum mechanics while the rest of the interaction energy is computed by molecular mechanics. Numerical studies are carried out to calculate torsional energies of six polypeptides using the GMFCC/MM approach and the energies are shown to be in general good agreement with the full system quantum calculation. Among those we tested is a polypeptide containing 396 atoms whose energies are computed at the MP26-31G* level. Our study shows that using GMFCC/MM, it is possible to perform high level ab initio calculation such as MP2 for applications such as structural optimization of protein complex and molecular dynamics simulation.     

Molecular Dynamics Simulations for Effects of Fluoropolymer Binder Content in CL-20/TNT Based Polymer-Bonded Explosives

In order to better understand the role of binder content, molecular dynamics (MD) simulations were performed to study the interfacial interactions, sensitivity and mechanical properties of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT) based polymer-bonded explosives (PBXs) with fluorine rubber F₂₃₁₁. The binding energy between CL-20/TNT co-crystal (1 0 0) surface and F₂₃₁₁, pair correlation function, the maximum bond length of the N–NO₂ trigger bond, and the mechanical properties of the PBXs were reported. From the calculated binding energy, it was found that binding energy increases with increasing F₂₃₁₁ content. Additionally, according to the results of pair correlation function, it turns out that H–O hydrogen bonds and H–F hydrogen bonds exist between F₂₃₁₁ molecules and the molecules in CL-20/TNT. The length of trigger bond in CL-20/TNT were adopted as theoretical criterion of sensitivity. The maximum bond length of the N–NO₂ trigger bond decreased very significantly when the F₂₃₁₁ content increased from 0 to 9.2%. This indicated increasing F₂₃₁₁ content can reduce sensitivity and improve thermal stability. However, the maximum bond length of the N–NO₂ trigger bond remained essentially unchanged when the F₂₃₁₁ content was further increased. Additionally, the calculated mechanical data indicated that with the increase in F₂₃₁₁ content, the rigidity of CL-20/TNT based PBXs was decrease, the toughness was improved.     

Assessing the performance of the molecular mechanics/Poisson Boltzmann surface area and molecular mechanics/generalized Born surface area methods. II. The accuracy of ranking poses generated from docking

In molecular docking, it is challenging to develop a scoring function that is accurate to conduct high-throughput screenings. Most scoring functions implemented in popular docking software packages were developed with many approximations for computational efficiency, which sacrifices the accuracy of prediction. With advanced technology and powerful computational hardware nowadays, it is feasible to use rigorous scoring functions, such as molecular mechanics/Poisson Boltzmann surface area (MM/PBSA) and molecular mechanics/generalized Born surface area (MM/GBSA) in molecular docking studies. Here, we systematically investigated the performance of MM/PBSA and MM/GBSA to identify the correct binding conformations and predict the binding free energies for 98 protein-ligand complexes. Comparison studies showed that MM/GBSA (69.4%) outperformed MM/PBSA (45.5%) and many popular scoring functions to identify the correct binding conformations. Moreover, we found that molecular dynamics simulations are necessary for some systems to identify the correct binding conformations. Based on our results, we proposed the guideline for MM/GBSA to predict the binding conformations. We then tested the performance of MM/GBSA and MM/PBSA to reproduce the binding free energies of the 98 protein-ligand complexes. The best prediction of MM/GBSA model with internal dielectric constant 2.0, produced a Spearman's correlation coefficient of 0.66, which is better than MM/PBSA (0.49) and almost all scoring functions used in molecular docking. In summary, MM/GBSA performs well for both binding pose predictions and binding free-energy estimations and is efficient to re-score the top-hit poses produced by other less-accurate scoring functions.