.. index:: single: Program; VibRot single: VibRot .. _UG\:sec\:vibrot: :program:`vibrot` ================= .. only:: html .. contents:: :local: :backlinks: none .. xmldoc:: %%Description: This program computes the vibrational-rotational spectrum of a diatomic molecule. In addition, spectroscopic constants are computed. The program can also compute transition probabilities and lifetimes for excited states. The program :program:`VIBROT` is used to compute a vibration-rotation spectrum for a diatomic molecule, using as input a potential computed over a grid. The grid should be dense around equilibrium (recommended spacing 0.05 au) and should extend to large distance (say 50 au) if dissociation energies are computed. The potential is fitted to an analytical form using cubic splines. The ro-vibrational Schrödinger equation is then solved numerically (using Numerov's method) for one vibrational state at a time and for a number of rotational quantum numbers as specified by input. The corresponding wave functions are stored on file :file:`VIBWVS` for later use. The ro-vibrational energies are analyzed in terms of spectroscopic constants. Weakly bound potentials can be scaled for better numerical precision. The program can also be fed with property functions, such as a dipole moment curve. Matrix elements over the ro-vib wave functions for the property in question are then computed. These results can be used to compute IR intensities and vibrational averages of different properties. :program:`VIBROT` can also be used to compute transition properties between different electronic states. The program is then run twice to produce two files of wave functions. These files are used as input in a third run, which will then compute transition matrices for input properties. The main use is to compute transition moments, oscillator strengths, and lifetimes for ro-vib levels of electronically excited states. The asymptotic energy difference between the two electronic states must be provided using the :kword:`ASYMptotic` keyword. .. index:: pair: Dependencies; VibRot .. _UG\:sec\:vibrot_dependencies: Dependencies ------------ The :program:`VIBROT` is free-standing and does not depend on any other program. .. index:: pair: Files; VibRot .. _UG\:sec\:vibrot_files: Files ----- Input files ........... The calculation of vibrational wave functions and spectroscopic constants uses no input files (except for the standard input). The calculation of transition properties uses :file:`VIBWVS` files from two preceding :program:`VIBROT` runs, redefined as :file:`VIBWVS1` and :file:`VIBWVS2`. Output files ............ :program:`VIBROT` generates the file :file:`VIBWVS` with vibrational wave functions for each :math:`v` and :math:`J` quantum number, when run in the wave function mode. If requested :program:`VIBROT` can also produce files :file:`VIBPLT` with the fitted potential and property functions for later plotting. .. index:: pair: Input; VibRot .. _UG\:sec\:vibrot_input: Input ----- This section describes the input to the :program:`VIBROT` program in the |molcas| program system. The program name is :: &VIBROT .. index:: pair: Keywords; VibRot Keywords ........ The first keyword to :program:`VIBROT` is an indicator for the type of calculation that is to be performed. Two possibilities exist: .. class:: keywordlist :kword:`ROVIbrational spectrum` :program:`VIBROT` will perform a vib-rot analysis and compute spectroscopic constants. .. xmldoc:: Note that only one of the above keywords can be used in a single calculation. If none is given the program will only process the input section. After this first keyword follows a set of keywords, which are used to specify the run. Most of them are optional. The compulsory keywords are: .. class:: keywordlist :kword:`ATOMs` Gives the mass of the two atoms. Write mass number (an integer) and the chemical symbol Xx, in this order, for each of the two atoms in free format. If the mass numbers is zero for any atom, the mass of the most abundant isotope will be used. All isotope masses are stored in the program. You may introduce your own masses by giving a negative integer value to the mass number (one of them or both). The masses (in unified atomic mass units, or Da) are then read on the next (or next two) entry(ies). The isotopes of hydrogen can be given as H, D, or T. .. xmldoc:: %%Keyword: ATOMs Read the mass number and chemical symbol of the atoms from the next line. If the mass number is zero the mass of the most abundant isotope will be used. Use a negative mass number to input the mass (in unified atomic mass units) in the next entry. :kword:`POTEntial` Gives the potential as an arbitrary number of lines. Each line contains a bond distance (in au) and an energy value (in au). A plot file of the potential is generated if the keyword :kword:`Plot` is added after the last energy input. One more entry should then follow with three numbers specifying the start and end value for the internuclear distance and the distance between adjacent plot points. This input must only be given together with the keyword :kword:`RoVibrational spectrum`. .. xmldoc:: %%Keyword: POTEntial Read the potential from a file (in au). Format: distance, value one pair on each line. Only together with vib-rot calculation. In addition you may want to specify some of the following optional input: .. class:: keywordlist :kword:`TITLe` One single title line .. xmldoc:: %%Keyword: TITLe One single title line :kword:`GRID` The next entries give the number of grid points used in the numerical solution of the radial Schrödinger equation. The default value is 199. The maximum value that can be used is 4999. .. xmldoc:: %%Keyword: GRID Give the number of numerical grid points (default is 199, max is 4999). :kword:`RANGe` The next entry contains two distances Rmin and Rmax (in au) specifying the range in which the vibrational wave functions will be computed. The default values are 1.0 and 5.0 au. Note that these values most often have to be given as input since they vary considerably from one case to another. If the range specified is too small, the program will give a message informing the user that the vibrational wave function is large outside the integration range. .. xmldoc:: %%Keyword: RANGe Give the range (Rmin-Rmax) in which the wave functions will be computed in atomic units. Default is 1.0-5.0 au. :kword:`VIBRational` The next entry specifies the number of vibrational quanta for which the wave functions and energies are computed. Default value is 3. .. xmldoc:: %%Keyword: VIBRational Specify the number of vibrational quanta (default is 3). :kword:`ROTAtional` The next entry specifies the range of rotational quantum numbers. Default values are 0 to 5. If the orbital angular momentum quantum number (:math:`m_\ell`) is non zero, the lower value will be adjusted to :math:`m_\ell` if the start value given in input is smaller than :math:`m_\ell`. .. xmldoc:: %%Keyword: ROTAtional Specify the range of rotational quantum numbers (default is 0-5). :kword:`ORBItal` The next entry specifies the value of the orbital angular momentum (0, 1, 2, etc.). Default value is zero. .. xmldoc:: %%Keyword: ORBItal Specify the orbital angular momentum:, 0, 1, 2, ... (default is 0). :kword:`SCALe` This keyword is used to scale the potential, such that the binding energy is 0.1 au. This leads to better precision in the numerical procedure and is strongly advised for weakly bound potentials. .. xmldoc:: %%Keyword: SCALe The potential will be scaled to a bond energy of 0.1 au. :kword:`NOSPectroscopic` Only the wave function analysis will be carried out but not the calculation of spectroscopic constants. .. xmldoc:: %%Keyword: NOSPectroscopic No calculation of spectroscopic constants. :kword:`OBSErvable` This keyword indicates the start of input for radial functions of observables other than the energy, for example the dipole moment function. The next line gives a title for this observable. An arbitrary number of input lines follows. Each line contains a distance and the corresponding value for the observable. As for the potential, this input can also end with the keyword :kword:`Plot`, to indicate that a file of the function for later plotting is to be constructed. The next line then contains the minimum and maximum R-values and the distance between adjacent points. When this input is given with the top keyword :kword:`RoVibrational spectrum` the program will compute matrix elements for vibrational wave functions of the current electronic state. Transition moment integrals are instead obtained when the top keyword is :kword:`Transition moments`. In the latter case the calculation becomes rather meaningless if this input is not provided. The program will then only compute the overlap integrals between the vibrational wave functions of the two states. The keyword :kword:`Observable` can be repeated up to ten times in a single run. All observables should be given in atomic units. .. xmldoc:: %%Keyword: OBSErvable Input for radial functions of observables (in au). The input is read from a file. The user is asked to read the users guide to learn how to construct this file. :kword:`TEMPerature` The next entry gives the temperature (in K) at which the vibrational averaging of observables will be computed. The default is 300 K. .. xmldoc:: %%Keyword: TEMPerature Temperature for vibrational averaging of observables (default is 300 K). :kword:`STEP` The next entry gives the starting value for the energy step used in the bracketing of the eigenvalues. The default value is 0.004 au (88 :math:`\text{cm}^{-1}`). This value must be smaller than the zero-point vibrational energy of the molecule. .. xmldoc:: %%Keyword: STEP Give the starting value for the energy step used in bracketing eigenvalues. Should be smaller than the zero point energy (default is 0.004 au). :kword:`ASYMptotic` The next entry specifies the asymptotic energy difference between two potential curves in a calculation of transition matrix elements. The default value is zero atomic units. .. xmldoc:: %%Keyword: ASYMptotic Specify the asymptotic energy difference between two potential curves in a calculation of transition matrix elements (default is 0.00 au). :kword:`ALLRotational` By default, when the :kword:`Transition moments` keyword is given, only the transitions between the lowest rotational level in each vibrational state are computed. The keyword :kword:`AllRotational` specifies that the transitions between all the rotational levels are to be included. Note that this may result in a very large output file. .. xmldoc:: %%Keyword: ALLRotational Include all rotational levels in a transition moments calculation. :kword:`PRWF` Requests the vibrational wave functions to be printed in the output file. .. xmldoc:: %%Keyword: PRWF Requests the vibrational wave functions to be printed. :kword:`DISTunit` Unit used for distances in the input potential. The default is `BOHR`. Other options include `ANGSTROM` and `PICOMETER`. The short form `PM` can also be used, instead of `PICOMETER`. .. xmldoc:: %%Keyword: DISTunit Specifies the unit used for distances in the input potential. :kword:`ENERunit` Unit used for energies in the input potential. The default is `HARTREE`. Other options include `ELECTRONVOLT`, `KCAL/MOL`, `KJ/MOL`, `CM-1`, and `MEGAHERTZ`. The short form `EV` can be used instead of `ELECTRONVOLT` and likewise `MHZ` can be used instead of `MEGAHERTZ`. .. xmldoc:: %%Keyword: ENERunit Specifies the unit used for energies in the input potential. Input example ............. :: &VIBROT RoVibrational spectrum Title = H2 (^1 Pi_u) Atoms = 0 H 0 H Potential 0.4233417991952784 -93390.8116364055 0.5291772489940979 -125520.5784258792 0.5820949738935077 -135202.0740308874 0.6350126987929174 -142230.7885620708 0.6879304236923273 -147325.2117261678 0.7408481485917370 -150985.4845047687 0.7937658734911469 -153567.9481018878 0.8466835983905567 -155331.6637865382 0.8996013232899664 -156468.2460791877 0.9525190481893763 -157121.6176632051 1.0054367730887860 -157401.2568735270 1.0583544979881960 -157391.4024626400 1.1112722228876060 -157157.4776230008 1.1641899477870150 -156750.6989542662 1.2700253975858350 -155571.7997582064 1.4816962971834740 -152450.7563927988 1.6933671967811130 -149070.0021134733 1.9050380963787530 -145873.2312217305 2.1167089959763920 -143043.6172437684 2.6458862449704900 -137805.7761879516 3.1750634939645880 -134764.6588985511 5.2917724899409790 -131360.0872323780 DistUnit = Angstrom EnerUnit = cm-1 Grid = 450 Range = 0.4 5.0 Vibrations = 3 Rotations = 1 4 Orbital = 1 Observable Dipole Moment 0.4233417991952784 0.57938359 0.5291772489940979 0.62852037 0.5820949738935077 0.65216622 0.6350126987929174 0.67506184 0.6879304236923273 0.69709869 0.7408481485917370 0.71821433 0.7937658734911469 0.73833904 0.8466835983905567 0.75741713 0.8996013232899664 0.77538706 0.9525190481893763 0.79219774 1.0054367730887860 0.80778988 1.0583544979881960 0.82211035 1.1112722228876060 0.83510594 1.1641899477870150 0.84672733 1.2700253975858350 0.86565481 1.4816962971834740 0.88532063 1.6933671967811130 0.88056207 1.9050380963787530 0.85474708 2.1167089959763920 0.81515210 2.6458862449704900 0.70549066 3.1750634939645880 0.62103112 5.2917724899409790 0.46501146 Plot = 1.0 10.0 0.1 Scale **Comments**: The vibrational-rotation spectrum for the :math:`^1\Pi_u` state of \ :math:`\ce{H2}` will be computed using the potential curve given in the input. The 3 lowest vibrational levels will be obtained and for each level for the rotational states in the range :math:`J`\=1 to 4. The mass for the most abundant isotope of :math:`\ce{H}` will be used. The vib-rot matrix elements of the dipole function will also be computed. A plot file of the potential and the dipole function will be generated. .. xmldoc::