Show pageOld revisionsBacklinksBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ====== Nuclear-electronic orbital (NEO) method ====== The [[https://doi.org/10.1021/acs.chemrev.9b00798|Nuclear-electron orbital (NEO)]] method pioneered by Hammes-Schiffer and coworkers is available in **''Molpro''** for density fitted spin-restricted NEO-Hartree-Fock as well as a local-density fitting variant. It allows to handle a selected number of hydrogen nuclei as quantum particles by building a second Fock-matrix for the latter, coupling both subsystems (electrons and quantum protons) by a Coulomb operator. Further information about the method can be found [[https://doi.org/10.1021%2Facs.jctc.3c01055|here]]. * **''DF-NEO-RHF'', //options//** calls the density-fitted NEO-Hartree-Fock program * **''LDF-NEO-RHF'', //options//** calls the local density-fitted NEO-Hartree-Fock program Currently, both options require the **''gdirect''** option and are not available with symmetry. ===== Density fitting NEO-Hartree-Fock ===== Using <code> DF-NEO-RHF, options </code> enables the density fitting NEO-RHF program. Through the density fitting approximation in the electronic subsystem as well as the Coulomb coupling the computational scaling for small to mid-size systems is drastically reduced. The calculation parameters can be fine tuned with the options described in [[the SCF program]] section and [[density fitting]] section. However, NEO calculations require some additional parameters explained in the following. ===== Local density fitting NEO-Hartree-Fock ===== Using <code> LDF-NEO-RHF, options </code> enables the local density fitting NEO-RHF program. The local density fitting of the electronic subsystem leads to further speed-ups in particular for large molecular systems. The specific parameters for local density fitting can be adjusted with the options given in the [[the SCF program#local density fitting Hartree-Fock]] section. ===== NEO specific options ===== ==== Basis sets ==== The basis definition for NEO calculations must be given accordingly to the following basis block layout <code> basis={ default=minao #Basis definition for the electronic subsystem set,nucbas default=neo-basis H1=pb4-f2 #Basis definition for the nuclear subsystem set,nucfit default=neo-basis H1=10s10p10d10f #Basis definition for the nuclear density fitting } </code> The electronic basis set can be freely chosen from the [[https://www.molpro.net/info/basis.php|Molpro basis set library]]. At the current stage no user defined mixed basis sets are possible within the NEO programs. The nuclear basis set is defined via the **''nucbas''** keyword. The default basis for nuclear basis sets must be defined in every case as the **''neo-basis''**. Afterwards, the selected NEO centers can be assigned with the desired basis set. It is highly recommended to use the specifically tailored [[https://doi.org/10.1063/5.0009233|PB basis sets]] for multicomponent methods developed by Hammes-Schiffer and coworkers. Note that all NEO centers need to be assigned individually with the same basis set. The density fitting basis for the nuclear subsystem is defined via the **''nucfit''** keyword. In order to avoid issues in basis set assignments for the classical nuclei, the default basis must be assigned as the **''neo-basis''**. Afterwards all NEO centers must be assigned the same fitting basis set (two have been included in the basis library), or a new set must be defined. For the fitting of the PB basis sets the even tempered 10s10p10d10f to 12s12p12d12f12g basis sets are recommended. ==== NEO centers ==== The desired NEO centers must be declared immediately before the NEO computation explicitly via <code> qnuc, H1, ... </code> Additionally, the chosen quantum mechanical nuclei must be given as first atoms in the geometry definition as shown for a water molecule below <code> 3 Water molecule with one NEO center H1 -3.5008791 1.2736107 0.7596000 O -3.9840791 1.3301107 -0.0574000 H -4.9109791 1.2967107 0.1521000 </code> ==== Starting options ==== In order to provide suitable starting orbitals for the NEO computation three options can be chosen. * The first option is to carry out a regular Hartree-Fock computation bevor the NEO program is called. Thereby, the program reads the electronic orbitals from the default RHF record. In order to give a specific record the **''START'', //record//** keyword in the NEO program input card can be employed. * The second option is especially beneficial for large systems, since the computational costs of a prior RHF calculation is avoided. One makes use of the natural orbitals from a diagonal density matrix constructed using atomic orbitals. Atomic occupation numbers are employed as electronic starting orbitals. This option can be used via the **''NEOATDEN''** keyword in the NEO program input card. * The third option is to start from a prior NEO computation via the **''NEOSTART'', //electronic record//, //nuclear record//** keyword. This can be used as a minimal-basis NEO guess for [[the SCF program#handling difficult cases: when the SCF cycle does not converge]]. ==== Thresholds ==== The thresholds for the NEO computation can be adjusted with the following keywords * **''NEOTHRE'', //number//** sets the overall NEO energy threshold for SCF convergence * **''NEOTHRIE'', //number//** sets the energy threshold for the electronic subsystem SCF convergence * **''NEOTHRIN'', //number//** sets the energy threshold for the nuclear subsystem SCF convergence * **''NEOTHRIG'', //number//** sets the gradient threshold for both subsystems * **''NEOTHRID'', //number//** sets the density threshold for both subsystems For robust convergence it is recommended to use higher thresholds for the SCF computations of both subsystems than the overall NEO energy. ==== Additional options ==== * **''NEOIT'', //iterations//** sets the overall NEO cycles * **''NEORD'', //number//** sets the start for the fast rotational update of the orbitals in the local version * **''NOBLOCKDIAG''** disables the block diagonalization of the nuclear starting guess (this is generally not recommended!!) * **''NEOMIXBAS''** enables the use of user-defined mixed basis sets (see example for use) ===== Adaptive NEO ===== Optimization of quantum nuclei positions with the adaptive NEO approach, where the nuclear centroids are computed on-the-fly during the SCF iterations. This procedure is available by using the <code> ADAPTIVE </code> keyword in the NEO program input card. ==== Threshold ==== The thresholds for the convergence criteria of the nuclear centers during an adaptive NEO computation can be adjusted with the following keyword * **''ADTHRES'', //number//** sets the convergence threshold for the nuclear centers in atomic units * **''ADITER'', //number//** sets the initial iteration for the start of the adaptive procedure (default=2) ==== Damping ==== The shift of the nuclear basis function center towards the charge centroid can be damped with the following keyword * **''ADDUMP'', //number//** sets the damping factor of the nuclear centroid shift ===== NEO examples ===== The first example shows the input of a **''DF-NEO-RHF''** calculation for a water molecule with two NEO centers starting with the **''NEOATDEN''** option and individual thresholds. <code> memory,50,m gdirect nosym geometry={ 3 H1 -3.5008791 1.2736107 0.7596000 H2 -4.9109791 1.2967107 0.1521000 O -3.9840791 1.3301107 -0.0574000 } charge=0 basis={ default=cc-pvdz set,nucbas default=neo-basis H1=pb4-f2 H2=pb4-f2 set,nucfit default=neo-basis H1=10s10p10d10f H2=10s10p10d10f } qnuc,H1,H2 {df-neo-rhf,maxdis=10,maxit=200,df_basis=cc-pvdz neothre,1.d-6 neothrie,1.d-7 neothrin,1.d-7 neothrg,1.d-7 neothrd,1.d-7 neoatden} </code> The second example shows the input of a **''LDF-NEO-RHF''** computation of the same molecule starting from a prior RHF calculation. In this example a [[dump_density_or_orbital_values_cube|cube]] file is requested. This will output the quantum nuclei density. <code> memory,50,m gdirect nosym geometry={ 3 H1 -3.5008791 1.2736107 0.7596000 H2 -4.9109791 1.2967107 0.1521000 O -3.9840791 1.3301107 -0.0574000 } charge=0 basis={ default=cc-pvdz set,nucbas default=neo-basis H1=pb4-f2 H2=pb4-f2 set,nucfit default=neo-basis H1=10s10p10d10f H2=10s10p10d10f } {rhf} qnuc,H1,H2 {ldf-neo-rhf,maxdis=10,maxit=200,df_basis=cc-pvdz} {cube,nuclear.cube;density,2102.2} </code> The following example shows a NEO calculation, where a user-defined mixed basis set is used. Thereby, the electronic basis set at the quantum nuclei is larger than for regular hydrogen atoms. The use of the **''NEOMIXBAS''** requires the additional definition of the **''elebas''** and **''elefit''** basis sets as shown below. <code> memory,50,m gdirect nosym geometry={ 3 H1 -3.5008791 1.2736107 0.7596000 H2 -4.9109791 1.2967107 0.1521000 O -3.9840791 1.3301107 -0.0574000 } charge=0 basis={ default=cc-pvtz H1=cc-pv5z set,nucbas default=neo-basis H1=pb4-f2 set,nucfit default=neo-basis H1=10s10p10d10f set,elebas default=cc-pvtz H1=cc-pv5z set,elefit,context=jkfit default=cc-pvtz H1=cc-pv5z } qnuc,H1 {df-neo-rhf,maxdis=10,maxit=1000,df_basis=elefit neoatden neomixbas } </code> The example below shows the input for an adaptive NEO calculation, where the nuclear basis function centers convergence is set below 1E-5 bohr and a damping factor of 0.5 is applied. <code> memory,50,m gdirect nosym geometry={ 3 H1 -3.5008791 1.2736107 0.7596000 H2 -4.9109791 1.2967107 0.1521000 O -3.9840791 1.3301107 -0.0574000 } charge=0 basis={ default=cc-pvdz set,nucbas default=neo-basis H1=pb4-f2 set,nucfit default=neo-basis H1=10s10p10d10f } qnuc,H1 {df-neo-rhf,maxdis=10,maxit=500,df_basis=cc-pvdz adaptive adthres,1.d-5 addump,0.5 } </code> ===== Bibliography ===== ===NEO methodology=== Simon P. Webb, Tzvetelin Iordanov, and Sharon Hammes-Schiffer [[https://doi.org/10.1063/1.1494980|Multiconfigurational nuclear-electronic orbital approach: Incorporation of nuclear quantum effects in electronic structure calculations]] //J. Chem. Phys.// **2002** //117// (9), 4106–4118. Fabijan Pavošević, Tanner Culpitt, and Sharon Hammes-Schiffer [[https://doi.org/10.1021/acs.chemrev.9b00798|Multicomponent Quantum Chemistry: Integrating Electronic and Nuclear Quantum Effects via the Nuclear–Electronic Orbital Method]] //Chemical Reviews// **2020** //120// (9), 4222-4253. ===PB basis sets=== Qi Yu, Fabijan Pavošević, and Sharon Hammes-Schiffer [[https://doi.org/10.1063/5.0009233|Development of nuclear basis sets for multicomponent quantum chemistry methods]] //J. Chem. Phys.// **2020** //152// (24), 244123. ===(L)DF-NEO-RHF=== Lukas Hasecke, and Ricardo A. Mata [[https://doi.org/10.1021/acs.jctc.3c01055|Nuclear Quantum Effects Made Accessible: Local Density Fitting in Multicomponent Methods]] //J. Chem. Theory Comput.// **2023** //19// (22), 8223–8233.