Application of semi-empirical and ab initio quantum mechanical calculations

1988 ◽  
Vol 2 (3) ◽  
pp. 223-224 ◽  
Author(s):  
Paul von Ragué Schleyer
Keyword(s):  
Ab Initio ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Semi Empirical

N2 positively charged defects in diamond. A quantum mechanical investigation of the structural, electronic, EPR and vibrational properties

2020 ◽  
Vol 8 (15) ◽  
pp. 5239-5247 ◽  
Author(s):  
Giulio Di Palma ◽  
Francesco Silvio Gentile ◽  
Valentina Lacivita ◽  
William C. Mackrodt ◽  
Mauro Causà ◽  
...  
Keyword(s):  
Ab Initio ◽  
Quantum Mechanical ◽  
Vibrational Properties ◽  
Quantum Mechanical Calculations ◽  
Mechanical Investigation ◽  
Crystal Code ◽  
Charged Defects ◽  
Positively Charged ◽  
Vibrational Characterization

Structural, EPR and vibrational characterization of the N2, N+2 and N++2 defects in diamond from ab initio quantum-mechanical calculations with the CRYSTAL code.

Crystal Structure and Tautomerism of 1-[N-(4-Iodophenyl)]aminomethylidene-2(1H)naphthalenone

2001 ◽  
Vol 56 (10) ◽  
pp. 1003-1008 ◽  
Author(s):  
H. Ünver ◽  
M. Kabak ◽  
D. M. Zengin ◽  
T. N. Durlu
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Quantum Mechanical ◽  
Monoclinic Space Group ◽  
Quantum Mechanical Calculations ◽  
X Ray ◽  
H Nmr ◽  
Mechanical Methods ◽  
Intramolecular Hydrogen ◽  
Semi Empirical

1-[N-(4-Iodophenyl)]aminomethylidene-2(1H)naphthalenone (1) (C17H12NOI) has been studied by X-ray analysis, IR, 1H NMR, UV and AM1 semi-empirical quantum mechanical methods. It crystallises in the monoclinic space group P21/n with a = 4.844(3), b = 21.428(2), c = 13.726(2) Å, ß = 93.07(2)° (R1 =0.032 for 4132 reflections [I > 2σ(I)]). The title compound is not planar and an intramolecular hydrogen bond connects O1 and N1 [2.530(4) Å]. Complementary IR, 1H NMR and UV measurements out. Tautomerism and conformations of the title semi-empirical quantum mechanical calculations and the results are compared with the X-ray data.

scholarly journals Accelerated Computation of Free Energy Profile at ab Initio Quantum Mechanical/Molecular Mechanics Accuracy via a Semi-Empirical Reference Potential. II. Recalibrating Semi-Empirical Parameters with Force Matching

2019 ◽  
Author(s):  
Xiaoliang Pan ◽  
Pengfei Li ◽  
Junming Ho ◽  
Jingzhi Pu ◽  
Ye Mei ◽  
...  
Keyword(s):  
Free Energy ◽  
Ab Initio ◽  
Quantum Mechanical ◽  
Energy Profile ◽  
Free Energy Profile ◽  
Force Matching ◽  
Energy Profiles ◽  
Reference Potential ◽  
Semi Empirical ◽  
Free Energy Profiles

An efficient and accurate reference potential simulation protocol is proposed for producing ab initio quantum mechanical molecular mechanical (AI-QM/MM) quality free energy profiles for chemical<br>reactions in a solvent or macromolecular environment. This protocol involves three stages: (a) using force matching to recalibrate a semi-empirical quantum mechanical (SE-QM) Hamiltonian for the specific reaction under study; (b) employing the recalibrated SE-QM Hamiltonian (in combination with molecular mechanical force fields) as the reference potential to drive umbrella samplings along the reaction pathway; and (c) computing AI-QM/MM energy values for collected configurations from the sampling and performing weighted thermodynamic perturbation to acquire AI-QM/MM corrected reaction free energy profile. For three model reactions (identity SN2 reaction, Menshutkin reaction, and glycine proton transfer reaction) in aqueous solution and one enzyme reaction (Claisen arrangement in chorismate mutase), our simulations using recalibrated PM3 SE-QM Hamiltonians well reproduced AI-QM/MM free energy profiles (at the B3LYP/6-31G* level of theory) all within 1 kcal/mol with a 20 to 45 fold reduction in the computer time.

scholarly journals Accelerated computation of free energy profile at ab initio quantum mechanical/molecular mechanical accuracy via a semi-empirical reference potential. II. Recalibrating semi-empirical parameters with force matching

2019 ◽  
Vol 21 (37) ◽  
pp. 20595-20605 ◽  
Author(s):  
Xiaoliang Pan ◽  
Pengfei Li ◽  
Junming Ho ◽  
Jingzhi Pu ◽  
Ye Mei ◽  
...  
Keyword(s):  
Free Energy ◽  
Ab Initio ◽  
Quantum Mechanical ◽  
Energy Profile ◽  
Force Matching ◽  
Energy Profiles ◽  
Reference Potential ◽  
Simulation Protocol ◽  
Semi Empirical ◽  
Free Energy Profiles

An efficient and accurate reference potential simulation protocol is proposed for producing ab initio quantum mechanical/molecular mechanical (AI-QM/MM) quality free energy profiles for chemical reactions in a solvent or macromolecular environment.

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