[{"data":1,"prerenderedAt":211},["ShallowReactive",2],{"page:\u002Farticles\u002Ftd-force-linear-angle-bend":3},{"id":4,"title":5,"author":6,"body":10,"cover":199,"date":200,"description":201,"extension":202,"head":203,"layout":204,"meta":205,"navigation":206,"path":207,"seo":208,"stem":209,"__hash__":210},"pages\u002Farticles\u002F45.td-force-linear-angle-bend.md","TD Force Calculation — \"Linear Angle in Bend\" Error",{"name":7,"avatarUrl":8,"link":9},"Likun Cai","https:\u002F\u002Favatars.githubusercontent.com\u002Fu\u002F103620968?v=4","https:\u002F\u002Fgithub.com\u002FAlchemist-Aloha",{"type":11,"value":12,"toc":196},"minimark",[13,20,26,34,39,52,57,60,65,68,85,90,100,103,108,111,121,124,131,138,143,158,163,169,174],[14,15,17],"h1",{"id":16},"td-force-calculation-linear-angle-in-bend-error",[18,19,5],"strong",{},[21,22,23],"p",{},[18,24,25],{},"Problem",[21,27,28,29,33],{},"The ",[30,31,32],"code",{},"Linear angle in Bend"," error repeatedly occurs during the TD force calculation for the triplet state of the IDT–ZnP molecule.",[21,35,36],{},[18,37,38],{},"Initial observation",[40,41,42,46,49],"ul",{},[43,44,45],"li",{},"When the Gaussian log file is opened in GaussView, the automatically generated connectivity\u002FZ-matrix appears unusual.",[43,47,48],{},"Several angles close to 179° are defined between atoms or groups that are not directly bonded.",[43,50,51],{},"This initially suggested that incorrect molecular connectivity might be causing Gaussian to construct problematic internal coordinates.",[21,53,54],{},[18,55,56],{},"Connectivity test",[21,58,59],{},"In GaussView, used:",[21,61,62],{},[30,63,64],{},"Atom List Editor → Edit → Reconnect All Atoms by Bonding",[21,66,67],{},"After reconnection:",[40,69,70,73,76,79],{},[43,71,72],{},"The molecular connectivity appeared more reasonable.",[43,74,75],{},"The remaining nearly linear angles corresponded primarily to physically meaningful bonds, especially the triple-bond bridges.",[43,77,78],{},"New Gaussian inputs were generated with explicit connectivity appended below the Cartesian coordinates.",[43,80,81,84],{},[30,82,83],{},"Opt + Freq"," and TD force calculations were then repeated.",[21,86,87],{},[18,88,89],{},"Result",[21,91,92,93,96,97,99],{},"Explicitly correcting and providing the molecular connectivity did ",[18,94,95],{},"not"," resolve the ",[30,98,32],{}," error.",[21,101,102],{},"This indicates that the problem is probably not caused by incorrect bond connectivity itself.",[21,104,105],{},[18,106,107],{},"Working solution",[21,109,110],{},"Using",[112,113,118],"pre",{"className":114,"code":116,"language":117},[115],"language-text","Geom=(Checkpoint,GIC)\n","text",[30,119,116],{"__ignoreMap":120},"",[21,122,123],{},"for the TD force calculation successfully avoids the error.",[21,125,126,127,130],{},"The issue therefore appears to originate from Gaussian's default ",[18,128,129],{},"redundant internal coordinate (RIC)"," representation. The nearly linear geometries associated with the triple-bond bridges can produce problematic bending coordinates in the default RIC set.",[21,132,133,134,137],{},"Using ",[18,135,136],{},"GIC (Generalized Internal Coordinates)"," for the force calculation prevents the problematic linear-bend coordinate from causing the calculation to fail.",[21,139,140],{},[18,141,142],{},"Current workflow",[144,145,146,149,152,155],"ol",{},[43,147,148],{},"Perform geometry optimization using the default RIC coordinates.",[43,150,151],{},"Perform the frequency calculation using the default RIC coordinates.",[43,153,154],{},"Use the resulting checkpoint file for the excited-state TD force calculation.",[43,156,157],{},"Run the TD force step with:",[112,159,161],{"className":160,"code":116,"language":117},[115],[30,162,116],{"__ignoreMap":120},[144,164,166],{"start":165},5,[43,167,168],{},"Use the resulting force information for the final resonance Raman (RR) calculation.",[21,170,171],{},[18,172,173],{},"Conclusion",[40,175,176,179,182,185,190],{},[43,177,178],{},"Explicit molecular connectivity does not fix the problem.",[43,180,181],{},"The optimized structure and frequency calculation using the default RIC coordinates appear to be valid.",[43,183,184],{},"The failure is specific to force generation when Gaussian encounters nearly linear bending coordinates in the default RIC representation.",[43,186,187,188,99],{},"Switching the TD force calculation to GIC successfully resolves the ",[30,189,32],{},[43,191,192,193,195],{},"Therefore, it appears acceptable to retain the default RIC-based ",[30,194,83],{}," results for the final RR calculation while using GIC specifically for the TD force step.",{"title":120,"searchDepth":197,"depth":197,"links":198},2,[],"\u002Farticles\u002Ftd-force-linear-angle-cover.webp","2026-08-17T00:00:00.000Z","Fixing Gaussian's \"Linear angle in Bend\" error in TD force calculations for the IDT–ZnP triplet state using Geom=(Checkpoint,GIC) instead of the default redundant internal coordinates.","md",{"title":5},"page",{},true,"\u002Farticles\u002Ftd-force-linear-angle-bend",{"title":5,"description":201},"articles\u002F45.td-force-linear-angle-bend","JZhLZyzI5ADLPZicDFVCXn8FtXvV_ny3WNIgABR-UR4",1786980373675]