| Summary: | Modifications to improve thinning approximation (TA) were considered in order to calculate two-dimensional scattering patterns (2DSPs) for dissipative particle dynamics (DPD) simulations of polymer melts under a shear flow. We proposed multipoint TA and adaptive TA because the bond lengths in DPD chains vary widely when compared to those in Kremer⁻Grest (KG) chains, and the effectiveness of these two types of TA for the two major DPD parameter sets were investigated. In this paper, we report our findings on the original DPD model with soft bonds and that with rigid bonds. Based on the behavior of the 2DSPs and the distribution of orientations of the bond vectors, two spot patterns originating from the oriented chain correlations were observed when distinct distributions of the highly oriented bond vectors in the shear direction were obtained. For multipoint TA, we concluded that at least two additional midpoints (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>mid</mi> </mrow> </msub> <mo>≥</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </semantics> </math> </inline-formula> are required to clearly observe the two spot patterns. For adaptive TA, a dividing distance of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>l</mi> <mrow> <mi>ATA</mi> </mrow> </msub> <mo>≤</mo> <mn>0.4</mn> </mrow> </semantics> </math> </inline-formula> is sufficient for clear observation, which is consistent with the requirement of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>mid</mi> </mrow> </msub> <mo>≥</mo> <mn>2</mn> </mrow> </semantics> </math> </inline-formula> for multipoint TA.
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