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More documentation on PP generation
git-svn-id: http://qeforge.qe-forge.org/svn/q-e/trunk/espresso@6877 c92efa57-630b-4861-b058-cf58834340f0
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giannozz
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@ -16,6 +16,8 @@ Universit\`a di Udine and IOM-Democritos, Trieste\\
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URL: {\tt http://www.fisica.uniud.it/$\thicksim$giannozz}}
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\maketitle
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\date
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\tableofcontents
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\section{Introduction}
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When I started to do my first first-principle calculation
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@ -662,7 +664,8 @@ from the origin, in the energy range \texttt{eminld=-2.0} Ry to
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In the \texttt{\&inputp} namelist, we specify the we want a single-projector,
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NC-PP (\texttt{pseudotype=1}), with nonlinear core correction
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(\texttt{nlcc=.true.}), using the $l=1$ channel as local (\texttt{lloc=1}).
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The output PP wil be written in UPF format to file \texttt{Ti.pbe-rrkj.UPF}.
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The output PP wil be written in UPF format to file \texttt{Ti.pbe-n-rrkj.UPF}
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(following the {\sc quantum ESPRESSO} convention for PP names).
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Following the two namelists, there is a list of states used for pseudization:
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the 4S state, with pseudization radius $r_c=2.9$ a.u.; the 3D state,
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$r_c=1.3$ a.u.; the 4P, $r_c=2.9$ a.u., listed as last because it is
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@ -675,7 +678,7 @@ the channel to be chosen as local potential.
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/
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&inputp
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pseudotype=1, nlcc=.true., lloc=1,
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file_pseudopw='Ti.pbe-rrkj.UPF',
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file_pseudopw='Ti.pbe-n-rrkj.UPF'
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/
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3
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4S 1 0 2.00 0.00 2.9 2.9
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@ -783,7 +786,7 @@ namelist):
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iswitch=2
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/
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&test
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file_pseudo='Ti.pbe-rrkj.UPF',
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file_pseudo='Ti.pbe-n-rrkj.UPF',
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nconf=1, configts(1)='3d2 4s2 4p0',
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ecutmin=50, ecutmax=200, decut=50
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/
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@ -823,7 +826,7 @@ So our data for PP generation are as follows:
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/
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&inputp
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pseudotype=1, nlcc=.true., lloc=0,
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file_pseudopw='Ti.pbe-rrkj.UPF',
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file_pseudopw='Ti.pbe-n-rrkj.UPF',
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/
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3
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4P 2 1 0.00 0.00 2.9 2.9
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@ -877,7 +880,7 @@ allows to test several configurations in the following way:
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iswitch=2
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/
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&test
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file_pseudo='Ti.pbe-rrkj.UPF',
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file_pseudo='Ti.pbe-n-rrkj.UPF',
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nconf=10
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configts(1)='3d2 4s2 4p0'
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configts(2)='3d2 4s1 4p1'
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@ -985,8 +988,108 @@ on eigenvalues$<5$ mRy. Configurations with different $3d$ occupancy,
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however, have errors one order of magnitude higher. For the extreme
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case of Ti$^{4+}$, the error is $\sim$ 0.1 Ry.
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\newpage
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In order to better understand what is going on, let us have a
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look at the AE vs PS orbitals and logarithmic derivatives for
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configuration 10 (i.e. for the bare PP). Let us add a line
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like this:
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\begin{verbatim}
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rlderiv=2.90, eminld=-4.0, emaxld=0.0, deld=0.01, nld=3,
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\end{verbatim}
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and plot files \texttt{ld10ps.wfc}, \texttt{ld10.dlog},
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\texttt{ld10ps.dlog} using \texttt{gnuplot} as above :
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\includegraphics[width=7.5cm]{pseudo-gen-fig3.pdf}
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\includegraphics[width=7.5cm]{pseudo-gen-fig4.pdf}
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Both the orbitals and the logarithmic derivatives (note the
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different energy range) start to exhibit some visible
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discrepancy now.
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One can try to fiddle with all generation parameters,
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better if one at the time, to see whether things improve.
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Curiously enough, the pseudization radius for the core
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correction, which in principle should be as small as
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possible, seems to improve things if pushed slightly
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outwards (try \texttt{rcore=2.0}). Also surprisingly,
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a smaller pseudization radius for the $3d$ state, 0.9
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or 1.0 a.u., doesn't bring any visible improvement
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to transferability
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(but it increases a lot the required cutoff!).
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Changing the pseudization radii for $4s$ and $4p$ states
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doesn't affect much the results.
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A different local potential -- a pseudized version
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of the total self-consistent potential -- can be chosen
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by setting \texttt{lloc=-1} and setting \texttt{rcloc}
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to the desired pseudization radius (a.u.). For small
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\texttt{rcloc} ghosts re-appear, but \texttt{rcloc=2.5}
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yields slightly better results. Note that the PP so
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generated will also have a $s$ projector, while the previous
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ones had only $p$ and $d$ projectors.
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One could also generate the PP from a different electronic
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configuration. Since Ti tends to lose rather than to attract
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electrons, it will be more easily found in a ionized state than
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in the neutral one. One might for instance use the electronic
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configuration of the Bachelet-Hamann-Schl\"uter paper\cite{BHS}:
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$3d^2 4s^{0.75} 4p^{0.25}$. This however doesn't seem to improve
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much. Finally we end up with these generation data:
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\begin{verbatim}
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&input
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atom='Ti', dft='PBE', config='[Ar] 3d2 4s2 4p0',
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iswitch=3
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/
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&inputp
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pseudotype=1, nlcc=.true., rcore=2.0, lloc=-1, rcloc=2.5,
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file_pseudopw='Ti.pbe-n-rrkj.UPF'
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/
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3
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4P 2 1 0.00 0.00 2.9 2.9
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3D 3 2 2.00 0.00 1.3 1.3
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4S 1 0 2.00 0.00 2.9 2.9
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\end{verbatim}
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\subsection {Single-projector, norm-conserving, with semicore states}
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The results of transferability tests suggest that a Ti PP with only
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$3d$, $4s$, $4p$ states have limited transferability to cases with
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different $3d$ configurations. In order to improve it, a possible
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way is to put semicore $3s$ and $3p$ states in valence. The maximum
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for those states (0.87 a.u. and 0.90 a.u. respectively) is in the
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same range as for $3d$ (0.98 a.u.). Let us try thus the following:
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\begin{verbatim}
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&input
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atom='Ti', dft='PBE', config='[Ar] 3d2 4s2 4p0',
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rlderiv=2.90, eminld=-4.0, emaxld=2.0, deld=0.01, nld=3,
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iswitch=3
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/
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&inputp
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pseudotype=1, lloc=-1, rcloc=2.5, rho0=0.001
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file_pseudopw='Ti.pbe-sp-rrkj.UPF'
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/
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3
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3S 1 0 2.00 0.00 1.1 1.1
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3P 2 1 6.00 0.00 1.2 1.2
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3D 3 2 2.00 0.00 1.3 1.3
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&test
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configts(1)='3s2 3p6 3d2 4s2 4p0',
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/
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\end{verbatim}
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Note the presence of the \texttt{\&test} namelist: it is used in this
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context to supply the electronic valence configuration, to be used
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for unscreening. As a first step, we do not include the core correction
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\newpage
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\subsection{Testing in molecules and solids}
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Even if our PP looks good
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(or not too bad) on paper based on the results of atomic calculations,
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it is always a good idea to test it in simple molecular or solid-state
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systems, for which all-electron data (i.e. calculations performed with
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the same XC functional but without PP's, such as e.g. FLAPW, LMTO,
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Quantum Chemstry calculations) is available. The comparison with
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experiments is of course interesting, but the goal of PP's is to
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reproduce AE data, not to improve DFT.
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\appendix
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