.. include:: autodoc_abbr_options_c.rst .. index:: molecule; specification .. _`sec:moleculeSpecification`: =================================== Molecule and Geometry Specification =================================== Coordinates =========== |PSIfour| has a very flexible input parser that allows the user to provide geometries as Cartesian coordinates, Z-matrix variables, or a combination of both. The use of fixed values and variables are supported for both. For example, the geometry for H\ :sub:`2` can be specified a number of ways, using the :samp:`molecule {optional_molecule_name} \\{...\\}` block. :: molecule { H H 1 0.9 } or :: molecule { H H 1 r r = 0.9 } or :: molecule { H1 H2 H1 0.9 } or :: molecule { H 0.0 0.0 0.0 H 0.0 0.0 0.9 } or :: molecule { H 0.0 0.0 0.0 H 0.0 0.0 r r = 0.9 } or :: molecule { H 0.0 0.0 -r H 0.0 0.0 r r = 0.45 } Blank lines are ignored and, unlike regular Python syntax, indentation within the molecule block does not matter, although the ``molecule`` keyword itself must be aligned within the input according to standard Python syntax. For more examples of geometry specification, see the :srcsample:`mints1` input file in the samples folder. It is also possible to mix Cartesian and Z-matrix geometry specifications, as demonstrated in the :srcsample:`mints4` and :srcsample:`mints6` sample input files. For example, consider the following geometry specification, taken from the :srcsample:`mints6` input:: molecule alanine { N -1.527107413251 0.745960643462 0.766603000356 C -0.075844098953 0.811790225041 0.711418672248 C 0.503195220163 -0.247849447550 -0.215671574613 O -0.351261319421 -0.748978309671 -1.089590304723 O 1.639498336738 -0.571249748886 -0.174705953194 H -1.207655674855 -0.365913941094 -0.918035522052 # First, remove the H from the alpha carbon. This line could be deleted # and is only included for completeness #H 0.429560656538 0.717651915252 1.673774709694 # Now patch it, using a Z Matrix specification. This patch can be applied # anywhere in the coord specification, as long as it appears lower than # the atoms referenced, as is usual for Z-Matrices C 2 rCC 3 aCCC 1 dCCCN H 7 rCH1 2 aHCC1 3 dHCCC1 H 7 rCH2 2 aHCC2 3 dHCCC2 H 7 rCH3 2 aHCC3 3 dHCCC3 H 0.221781602033 1.772570540211 0.286988509018 H -1.833601608592 0.108401996052 1.481873213172 H -1.925572581453 1.640882152784 0.986471814808 aCCC = 108.0 rCC = 1.4 dCCCN = 120 rCH1 = 1.08 rCH2 = 1.08 rCH3 = 1.08 aHCC1 = 109.0 aHCC2 = 109.0 aHCC3 = 109.0 dHCCC1 = 0.0 dHCCC2 = 120.0 dHCCC3 = 240.0 } Here, we remove the hydrogen from the alpha carbon of glycine and replace it with a methyl group. Applying this patch using Cartesian coordinates is difficult, because it depends on the orientation of the existing glycine unit. In this example, we use Z-Matrix coordinates to define the methyl group, and define the orientation in terms of the existing glycine Cartesian coordinates which is much easier to visualize than the corresponding Cartesian-only approach. .. index:: molecule; multiple in input file .. _`sec:multipleMolecules`: .. index:: triple: setting; keywords; molecule pair: molecule; charge pair: molecule; multiplicity pair: molecule; symmetry pair: molecule; no_reorient pair: molecule; units .. _`sec:moleculeKeywords`: Molecule Keywords ================= In addition to specifying the geometry, additional information can be provided in the molecule block :samp:`molecule {optional_molecule_name} \\{...\\}`. **Charge & Multiplicity** If two integers :samp:`{charge} {multiplicity}` are encountered on any line of the molecule block, they are interpreted as the molecular charge and multiplicity (:math:`2 M_s + 1`), respectively. For multi-fragment complexes, each fragment can have a :samp:`{charge} {multiplicity}` line. **Units** By default, |Angstrom| units are used; this is changed by adding a line that reads :samp:`units {spec}`, where :samp:`{spec}` is one of ``ang``, ``angstrom``, ``a.u.``, ``au``, or ``bohr``. **Orientation** Certain computations require that the molecule is not reoriented. This can be achieved by adding either ``no_reorient`` or ``noreorient``. To prevent even recentering of the molecule, add ``no_com`` or ``nocom``. **PubChem** A line reading :samp:`pubchem:{mol}` fetches the geometry for molecule :samp:`{mol}` from the PubChem database, where :samp:`{mol}` is either the IUPAC molecule name or the CID number. See :ref:`sec:pubchem` for details. **Symmetry** The symmetry can be specified by a line reading :samp:`symmetry {symbol}`, where :samp:`{symbol}` is the Sch\ |o_dots|\ nflies symbol of the (Abelian) point group to use for the computation, one of one of ``c1``, ``c2``, ``ci``, ``cs``, ``d2``, ``c2h``, ``c2v``, or ``d2h``. This need not be specified, as the molecular symmetry is automatically detected by |PSIfour|. See :ref:`sec:symmetry` for details. **Fragments** A line reading ``--`` is interpreted as the separator between two non-covalently bound molecular fragments. See :ref:`sec:fragments` for details. Multiple Molecules ================== To facilitate more elaborate computations, it is possible to provide a name for each molecule and tell |PSIfour| which one should be used in a given calculation. For example, consider the following input file:: molecule h2 { H H 1 0.9 } set basis cc-pvdz set reference rhf energy('scf') # on H2 clean() molecule h { H } set basis cc-pvdz set reference uhf energy('scf') # on H Here, two separate jobs are performed on two different molecules; the first is performed on H\ :sub:`2`, while the second is for H atom. The last molecule to be specified is the "active" molecule by default. To explicitly activate a named molecule, the activate command is provided. With it, the above input file can be equivalently written as follows. Alternatively, the molecule can be specified directly to the computing function. Below, the third calculation is the same as the first. :: molecule h2 { H H 1 0.9 } molecule h { H } activate(h2) set basis cc-pvdz set reference rhf energy('scf') # on H2 clean() activate(h) set basis cc-pvdz set reference uhf energy('scf') # on H # -------------------------------------- # equivalent to previous input ends here clean() set reference rhf energy('scf', molecule=h2) # on H2 :ref:`sec:jobControl` provides more details about the job control and calculation keywords used in the above examples. .. index:: single: Ghost Atoms single: molecule; ghost .. _`sec:ghosts`: Ghost Atoms =========== While many common computations, particularly SAPT and counterpoise corrections, can be greatly simplified using the notation described in :ref:`sec:fragments`, manual specification of ghost atoms is sometimes required. Either :: molecule he2 { He Gh(He) 1 2.0 } or :: molecule he2 { He @He 1 2.0 } will generate a helium dimer with the second atom ghosted, *i.e.*, possessing basis functions but no electrons or nuclear charge. See :srcsample:`dfmp2_1` and :srcsample:`ghosts` for a demonstration of both mechanisms for specifying ghost atoms. .. index:: single: Isotopes single: molecule; isotope .. _`sec:isotope`: Isotopic Substitution ===================== .. caution:: Use of isotopic substitution in |PSIfour| is not well developed, and the syntax is subject to change. At present, isotopes can only be specified at creation-time of the molecule The syntax for a deuterium- and tritium-substituted water is below. Note that asymmetric isotopic substitution such as this *will* change the molecule's point group symmetry. :: molecule dto { units au O 0.00000000 0.00000000 0.00000000 H@2.014101779 0.00000000 1.93042809 -1.10715266 H_label@3.01604927 0.00000000 -1.93042809 -1.10715266 } The masses used by |PSIfour| can be found at :source:`include/masses.h`. See :srcsample:`freq-isotope` for about the only use to which isotopologs can presently be put in |PSIfour|. .. index:: single: PubChem single: molecule; PubChem .. _`sec:pubchem`: `PubChem `_ Database ====================================================== Obtaining rough starting guess geometries can be burdensome. The Z-matrix coordinate system was designed to provide chemists with an intuitive method for guessing structures in terms of bond lengths and angles. While Z-matrix input is intuitive for small molecules with few degrees of freedom, it quickly becomes laborious as the system size grows. To obtain a reasonable starting guess geometry, |PSIfour| can take a chemical name as input; this is then used to attempt to retrieve Cartesian coordinates from the [PubChem]_ database. For example, to run a computation on benzene, we can use the following molecule specification:: molecule benzene { pubchem:benzene } If the computer is connected to the internet, the above code will instruct |PSIfour| to search PubChem for a starting structure. The search is actually performed for compounds whose name *contains* "benzene", so multiple entries will be returned. If the name provided ("benzene" in the above example) exactly matches one of the results, that entry will be used. If no exact match is found the results, along with a unique chemical identifier (CID), are printed to the output file, prompting the user to provide a more specific name. For example, if we know that we want to run a computation on a compound whose name(s) contain "benzene", but we're not sure of the exact IUPAC name, the following input can be used:: molecule benzene { pubchem:benzene* } Appending the "*" prevents an exact match from being found and, at the time of writing, the following results are displayed in the output file:: Chemical ID IUPAC Name 241 benzene 7371 benzenesulfonic acid 91526 benzenesulfonate 244 phenylmethanol 727 1,2,3,4,5,6-hexachlorocyclohexane 240 benzaldehyde 65723 benzenesulfonohydrazide 74296 N-phenylbenzenesulfonamide 289 benzene-1,2-diol 243 benzoic acid 7370 benzenesulfonamide 636822 1,2,4-trimethoxy-5-[(E)-prop-1-enyl]benzene 7369 benzenesulfonyl chloride 12932 N-[2-di(propan-2-yloxy)phosphinothioylsulfanylethyl]benzenesulfonamide 7505 benzonitrile 78438 N-[anilino(phenyl)phosphoryl]aniline 12581 3-phenylpropanenitrile 517327 sodium benzenesulfonate 637563 1-methoxy-4-[(E)-prop-1-enyl]benzene 252325 [(E)-prop-1-enyl]benzene Note that some of these results do not contain the string "benzene"; these compounds have synonyms containing that text. We can now replace the "benzene*" in the input file with one of the above compounds using either the IUPAC name or the CID provided in the list, *viz*:: molecule benzene { pubchem:637563 } or :: molecule benzene { pubchem:1-methoxy-4-[(E)-prop-1-enyl]benzene } Some of the structures in the database are quite loosely optimized and do not have the correct symmetry. Before starting the computation, |PSIfour| will check to see if the molecule is close to having each of the possible symmetries, and will adjust the structure accordingly so that the maximum symmetry is utilized. The standard keywords, described in :ref:`sec:moleculeKeywords`, can be used in conjuction to specify charge, multiplicity, symmetry to use, *etc.* . .. index:: symmetry, Cotton-ordering .. _`sec:symmetry`: Symmetry ======== For efficiency, |PSIfour| can utilize the largest Abelian subgroup of the full point group of the molecule. Concomitantly, a number of quantities, such as |globals__socc| and |globals__docc|, are arrays whose entries pertain to irreducible representations (irreps) of the molecular point group. Ordering of irreps follows the convention used in Cotton's :title:`Chemical Applications of Group Theory`, as detailed in Table :ref:`Irreps `. We refer to this convention as "Cotton Ordering" hereafter. .. _`table:irrepOrdering`: .. table:: Ordering of irreducible representations (irreps) used in |PSIfour| +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | Point Group | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +================+=============+================+================+================+=============+================+================+================+ | :math:`C_1` | :math:`A` | | | | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`C_i` | :math:`A_g` | :math:`A_u` | | | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`C_2` | :math:`A` | :math:`B` | | | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`C_s` | :math:`A'` | :math:`A''` | | | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`D_2` | :math:`A` | :math:`B_1` | :math:`B_2` | :math:`B_3` | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`C_{2v}` | :math:`A_1` | :math:`A_2` | :math:`B_1` | :math:`B_2` | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`C_{2h}` | :math:`A_g` | :math:`B_g` | :math:`A_u` | :math:`B_u` | | | | | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ | :math:`D_{2h}` | :math:`A_g` | :math:`B_{1g}` | :math:`B_{2g}` | :math:`B_{3g}` | :math:`A_u` | :math:`B_{1u}` | :math:`B_{2u}` | :math:`B_{3u}` | +----------------+-------------+----------------+----------------+----------------+-------------+----------------+----------------+----------------+ For example, water (:math:`C_{2v}` symmetry) has three doubly occupied :math:`A_1` orbitals, as well as one each of :math:`B_1` and :math:`B_2` symmetry; the corresponding |globals__docc| array is therefore:: DOCC = [3, 0, 1, 1] Although |PSIfour| will detect the symmetry automatically, and use the largest possible Abelian subgroup, the user might want to run in a lower point group. To do this the molecule keyword :samp:`symmetry {symbol}` can be used (see :ref:`sec:moleculeKeywords`). In most cases the standard Schönflies symbol (one of ``c1``, ``c2``, ``ci``, ``cs``, ``d2``, ``c2h``, ``c2v``, ``d2h`` will suffice for :samp:`{symbol}`. For certain computations, the user might want to specify which particular subgroup is to be used by appending a unique axis specifier. For example when running a computation on a molecule with :math:`D_{2h}` symmetry in :math:`C_{2v}`, the :math:`C_2` axis can be chosen as either the :math:`x`, the :math:`y`, or the :math:`z`; these can be specified by requesing the symmetry as ``c2vx``, ``c2vy``, or ``c2vz``, respectively. Likewise the ``c2x``, ``c2y``, ``c2z``, ``c2hx``, ``c2hy``, and ``c2hz`` labels are valid. For :math:`C_s` symmetry the labels ``csx``, ``csy``, and ``csz`` request the :math:`yz`, :math:`xz`, and :math:`xy` planes be used as the mirror plane, respectively. If no unique axis is specified, |PSIfour| will choose an appropriate subgroup. Certain types of finite difference computations, such as numerical vibrational frequencies, might lower the symmetry of the molecule. When this happens symmetry-dependent arrays, such as |globals__socc|, are automatically remapped to the lower symmetry. For example, if we were to investigate the :math:`^2B_1` state of water cation, we can specify SOCC = [0, 0, 1, 0] in the input file. If any ensuing computations lower the symmetry, the above array will be appropriately remapped. For example, reducing the symmetry to :math:`C_s` (with the molecular plane defining the mirror plane), the above array will be automatically interpreted as: SOCC = [0, 1] Some caution is required, however. The :math:`^2A_1` state can be obtained with the SOCC = [1, 0, 0, 0] specification, which would become SOCC = [1, 0] under the above-mentioned reduction in symmetry. The :math:`^2B_2` state, whose singly-occupied orbitals are SOCC = [0, 0, 0, 1] would be mapped to SOCC = [1, 0] which is the same occupation as the :math:`^2A_1` state. In this case, the :math:`^2A_1` state is lower in energy, and is not problematic. The distorted geometries for the :math:`^2B_2` state are excited states that are subject to variational collapse. One way to obtain reliable energies for these states is to use a multi-state method; in this case it's easier to run the entire computation in the lowest symmetry needed during the finite difference procedure. .. index:: molecule; multiple fragments .. _`sec:fragments`: Non-Covalently Bonded Molecule Fragments ======================================== |PSIfour| has an extensive range of tools for treating non-covalent intermolecular forces, including counterpoise corrections and symmetry adapted perturbation theory methods. These require the definition of which fragments are interacting within the complex. |PSIfour| provides a very simple mechanism for doing so: simply define the complex's geometry using the standard Cartesian, Z-matrix, or mixture thereof, specifications and then place two dashes between nonbonded fragements. For example, to study the interaction energy of ethane and ethyne molecules, we can use the following molecule block:: molecule eneyne { 0 1 C 0.000000 -0.667578 -2.124659 C 0.000000 0.667578 -2.124659 H 0.923621 -1.232253 -2.126185 H -0.923621 -1.232253 -2.126185 H -0.923621 1.232253 -2.126185 H 0.923621 1.232253 -2.126185 -- 0 1 C 0.000000 0.000000 2.900503 C 0.000000 0.000000 1.693240 H 0.000000 0.000000 0.627352 H 0.000000 0.000000 3.963929 } In this case, the charge and multiplicity of each interacting fragment is explicitly specified. If the charge and multiplicity are specified for the first fragment, it is assumed to be the same for all fragments. When considering interacting fragments, the overall charge is simply the sum of all fragment charges, and any unpaired electrons are assumed to be coupled to yield the highest possible :math:`M_s` value. Having defined a molecule containing fragments like ``eneyne`` above, it is a simple matter to perform calculations on only a subset of the fragments. For instance, the commands below run a scf first on the ethene fragment alone (``extract_subsets(1)`` pulls out fragment 1 as Real atoms and discards remaining fragments) and next on the ethene fragment with the ethyne fragment ghosted (``extract_subsets(1,2)`` pulls out fragment 1 as Real atoms and sets fragment 2 as Ghost atoms). For beyond bimolecular complexes, arrays can be used, e.g. ``extract_subsets(2,[1,3])``:: mA = eneyne.extract_subsets(1) energy('scf') clean() mAcp = eneyne.extract_subsets(1,2) energy('scf') If the molecule contains fragments but is not conveniently ordered for the ``--`` marker, the :py:func:`~wrapper_autofrag.auto_fragments` function can be applied, as shown in :srcsample:`pywrap-basis`, to return as active molecule the previous active molecule, only fragmented. Advanced Python =============== A named molecule in an input file is a full-fledged instance of the powerful :ref:`C++ Molecule class `. Thus, all member functions (that have been exported via Boost Python) documented thereat are accessible through the handle :samp:`{option_molecule_name}` in :samp:`molecule {optional_molecule_name} \\{...\\}`. * The molecular geometry can be got and set and manipulated as a :ref:`psi4.Matrix ` object. Below shows how to access coordinates in an input file in Python. :: molecule formaldehyde { C 0.0 0.0 0.0 O 0.0 1.2 0.0 H -0.8 -0.3 0.0 H 0.8 -0.3 0.0 # set geometry in angstroms } formaldehyde.update_geometry() # update the molecule internals since pre-energy()-like call formaldehyde.print_out() # print molecule to output file geom1psi = formaldehyde.geometry() # get coordinates in bohr as a psi4.Matrix geom1psi.print_out() # print coordinates array to output file geom1py = mat2arr(geom1psi) # get coordinates as a Python array print geom1py # print coordinates to screen geom2py = [[ 0.0, 0.0, 0.0], [ 0.0, 1.5, 0.0], [-0.8, -0.3, 0.0], [ 0.8, -0.3, 0.0]] # define alternate coordinates in angstroms as Python array geom2psi = psi4.Matrix(4, 3) # initialize psi4.Matrix geom2psi.set(geom2py) # load Python array into psi4.Matrix geom2psi.scale(1.0/psi_bohr2angstroms) # scale into bohr geom2psi.print_out() # print alternate coord array to output file formaldehyde.set_geometry(geom2psi) # load alternate coordinates into molecule formaldehyde.update_geometry() # update the molecule internals formaldehyde.print_out() # print new molecule to output file compare_values(28.9950517332, formaldehyde.nuclear_repulsion_energy(), 4, "geom2 took") * Molecules can be initited from XYZ files and fragmented for SAPT computations. :: # >>> cat mol1.xyz #7 # #O 0.00000000 -0.05786571 -1.47979303 #N 0.00000000 0.01436394 1.46454628 #H 0.00000000 0.82293384 -1.85541474 #H 0.81348351 0.39876776 1.92934049 #H 0.00000000 0.07949567 -0.51934253 #H 0.00000000 -0.98104857 1.65344779 #H -0.81348351 0.39876776 1.92934049 # >>> cat mol2.xyz # 6 au # stuff # C 0.00000000000000 0.00000000000000 5.26601138679877 # C 0.00000000000000 0.00000000000000 -3.15195886530135 # H 0.00000000000000 0.00000000000000 7.28558683837122 # H 0.00000000000000 0.00000000000000 -1.12178201232889 # N 0.00000000000000 0.00000000000000 3.08339310458383 # N 0.00000000000000 0.00000000000000 -5.33865984413460 sapt = {'mol1': -0.0105313323529, 'mol2': -0.00839486625709} nre = {'mol1': 38.8138764635, 'mol2': 72.3451968428} set basis jun-cc-pvdz for mol in ['mol1', 'mol2']: filen = mol + '.xyz' p4mol = Molecule.init_with_xyz(filen) # create molecule from file above fragmentedmol = auto_fragments(molecule=p4mol) # fragment with BFS algorithm activate(fragmentedmol) # activate returned molecule (for sapt) e = energy('sapt0') # run SAPT that requires 2 fragments compare_values(sapt[mol], e, 5, '%s sapt ok' % mol) compare_values(nre[mol], p4mol.nuclear_repulsion_energy(), 4, '%s ok' % mol) clean() # clean scratch between loop calcs * The essential element, mass and coordinate information of the molecule is accessible :: molecule eneyne { 0 1 C_ene 0.000000 -0.667578 -2.124659 C_ene 0.000000 0.667578 -2.124659 H_ene@2.014 0.923621 -1.232253 -2.126185 H_ene -0.923621 -1.232253 -2.126185 H_ene -0.923621 1.232253 -2.126185 Gh(H_ene) 0.923621 1.232253 -2.126185 -- 0 1 X 9.0 9.0 9.0 C_yne 0.000000 0.000000 2.900503 C_yne 0.000000 0.000000 1.693240 H_yne 0.000000 0.000000 0.627352 H_yne 0.000000 0.000000 3.963929 } eneyne.update_geometry() for iat in range(eneyne.natom()): print """{:4} {:4} {:12} {:8.4f} {:12.6f} {:12.6f} {:12.6f} {:12.6f}""".format( eneyne.Z(iat), # atomic number eneyne.symbol(iat), # element symbol eneyne.label(iat), # input element label eneyne.charge(iat), # element charge eneyne.x(iat), # x-coordinate eneyne.y(iat), # y-coordinate eneyne.z(iat), # z-coordinate eneyne.mass(iat), # mass ) # 6.0 C C_ENE 6.0000 -0.031900 -1.218981 -3.948079 12.000000 # 6.0 C C_ENE 6.0000 -0.031900 1.304098 -3.948079 12.000000 # 1.0 H H_ENE 1.0000 1.713491 -2.286062 -3.950962 2.014000 # 1.0 H H_ENE 1.0000 -1.777290 -2.286062 -3.950962 1.007825 # 1.0 H H_ENE 1.0000 -1.777290 2.371180 -3.950962 1.007825 # 0.0 H H_ENE 0.0000 1.713491 2.371180 -3.950962 1.007825 # 6.0 C C_YNE 6.0000 -0.031900 0.042559 5.548101 12.000000 # 6.0 C C_YNE 6.0000 -0.031900 0.042559 3.266705 12.000000 # 1.0 H H_YNE 1.0000 -0.031900 0.042559 1.252468 1.007825 # 1.0 H H_YNE 1.0000 -0.031900 0.042559 7.557685 1.007825