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.IP "\fB:DBOC:DISPLACEMENT =\fP \fIreal\fP"
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Determines the finite difference step (in a.u.). The default is 0.0005 a.u.
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.IP "\fB:DBOC:DISP_PER_COORD =\fP \fIinteger\fP"
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Determines the number of displacements for each coordinate. Set it to 2 to compute
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DBOC with standard accuracy (enough significant digits for up to second derivatives;
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DBOC accurate to square of displacement size),
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and 4 to compute DBOC with improved accuracy (DBOC accurate to the fourth power of displacement size).
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.IP "\fB:DBOC:ISOTOPES =\fP \fIstring_vector\fP"
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Specifies which isotope to use for each atom. Each string should specify
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an isotope label as defined in \fBinclude/masses.h\fP. By default,
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This keyword should only be used by advanced users who are familiar with
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how DBOC is evaluated by finite differences.
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The keyword may be used to specify the cartesian nuclear coordinates
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to use in the sum expression for DBOC and their respective coefficients.
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to use in the sum expression for DBOC, their respective coefficients,
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and whether they are symmetric or nonsymmetric with respect displacements.
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doesn't currently use symmetry to reduce the number of displacements,
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however, all computations are performed in the highest Abelian point group.
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Hence this keyword can be used to reduce the number of displacements and/or
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to specify the exact orbital occupations for specific displcements
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in case the occupation guess produced by
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The value for this keyword is an array of 2 element vectors. The first
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can use symmetry to minimize the number of wave function computations.
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Hence this keyword need only be used for diagnostic purposes or when
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displacements along different coordinates need to be run separately (e.g.
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require different occupation vectors).
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The value for this keyword is an array of 3 element vectors. The first
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element of each vector is the index of the cartesian coordinate which to include
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into the sum and the second element is a real coefficient for
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the respective term in the DBOC expression. Indices are C-style, i.e.
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from 0 to 3*natom-1. By default derivative along each Cartesian coordinate
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comes into DBOC expression with coefficient 1.0.
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into the sum. The second element is a real coefficient for
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the respective term in the DBOC expression. The third element is
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a string that can take two values, \fIsymm\fP and \fInonsymm\fP,
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which indicate that the coordinate is symmetric or nonsymmetric
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with respect to displacements, respectively.
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Indices are C-style, i.e. from 0 to 3*natom-1.