## 4 Conclusions  
LSD and its newly obtained analogs have been commonly found at crime scenes, and their analysis is a constant task for forensic investigators. Five functionals (B3 LYP, CAM-B3 LYP, B3 PW91, M05-2X, and M06-2X) in conjunction with a 6-311++G(d,p) basis set have been employed for the optimization of structure starting from a crystallographic LSD structure. The lowest mean absolute error (MAE) was calculated for the structure optimized at the M05-2X/6-311++G(d,p) level of theory with MAE of bond lengths and angles being 0.0436 A and 2.7\({}^{\circ}\). The correction factor (0.848) for IR wavenumbers was calculated by comparing the experimental and theoretical position of the C=O stretching vibration wavenumber. The rest of the bands were also well reproduced. The \({}^{13}\)C NMR spectrum was assigned, and a high correlation factor (0.999) was obtained for the experimental and theoretical data, with a mean absolute error of 2.0 ppm. Several methods for predicting UV-VIS spectrum were shown, with the optimization of ground and first excited state leading to the difference of 15 nm in the experimental and theoretical values. The most abundant mass fragments a\" 221' 207, 181, and 72 \(m/z\) were optimized. Their stability was explained by the restored planarity of the fragment and formation of the six- and four-membered rings with extended delocalization. These results coincided adequately with the mass spectrum of the seized real sample. Mentioned level of theory was applied for the optimization of two LSD analogs with 2-pentyl and 2-hexyl moieties. MAE values for the bond lengths and angles were around 0.02 A and 1\({}^{\circ}\), respectively. The 13C NMR spectra of two common analogs, 1-propionyl-d-lysergic acid diethylamide **(1P-LSD)** and 1-butanol-d-lysergic acid diethylamide **(1B-LSD)**, were predicted with correlation coefficients of 0.999 and MAE values lower than 2.5 ppm. These results prove the assumption that theoretical methods could be applied to the structural analysis of novel psychedelics based on the available spectra from the seized samples. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13052984/s1](https://www.mdpi.com/article/10.3390/app13052984/s1)]([https://www.mdpi.com/article/10.3390/app13052984/s1](https://www.mdpi.com/article/10.3390/app13052984/s1)), Table S1. Experimental and theoretical (different functionals with 6-311++G(d,p) basis set) bond lengths (in A) of **LSD**; Table S2. Experimental and theoretical (different functionals with 6-311++G(d,p) basis set) bond angles (in \({}^{\circ}\)) of **LSD**; Table S3. The assigned vibrations of LSD (at M05-2X/6-311++G(d,p) level of theory); Figure S1: Optimized structure of LSD tartrate (at M05-2X/6-311++G(d,p) level of theory); Figure S2: Optimized structure of the first excited state of LSD (at M05-2X/6-311++G(d,p) level of theory); Figure S3: Optimized structures (at M05-2X/6-311++G(d,p) level of theory) of LSD with one water molecule; Figure S4: GC-MS data of the seized sample; Table S4: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) bond lengths (in A) of **A1**; Table S5: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) bond angles (in \({}^{\circ}\)) of **A1**; Table S6: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) bond lengths (in A) of **A2**; Table S7: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) bond lengths (in \({}^{\circ}\)) of **A2**; Table S8: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) chemical shifts of **1P-LSD**; Table S9: Experimental and theoretical (at M05-2X/6-311++G(d,p) level of theory) chemical shifts of **1B-LSD**. Scheme S1: The atom numbering scheme for LSD. **Author Contributions:** Conceptualization, D.D. and J.D. ; methodology, D.D. and D.M. ; software, D.D., Z.M. and D.M. ; validation, J.D., M.M. and D.M. ; formal analysis, J.D. ; investigation, J.D. ; resources, D.D. ; data curation, M.M.