A document about the INPUT of davidson is added.

git-svn-id: http://qeforge.qe-forge.org/svn/q-e/trunk/espresso@10317 c92efa57-630b-4861-b058-cf58834340f0

TDDFPT/Doc/INPUT_Davdison.txt

@@ -0,0 +1,80 @@
+# Descriptions for the input of turbo_davidson.x
+# Created by Xiaochaun Ge (Jun. 2013)
+
+=====================================
+num_eign  Default: 1
+num_init  Default: 2
+
+Here you indicate the number of eigenstates that you would like to calculate at once.
+
+=====================================
+num_basis_max Default: 20
+
+The maximum number of basis that you allow for the sub basis set. One should notice 
+that the memory requirement of davidson algorithm is mainly determined by this variable. 
+An estimation of the memory is reported at the first of the run. 
+
+=====================================
+residue_conv_thr Default: 1.0E-4
+
+The convergence level of the residue.
+
+
+=====================================
+precondition  Default: .true.
+
+If or not use the precondition. At this moment, one sees no reason not to use precondition. 
+
+
+=====================================
+single_pole Default: .false.
+
+A slightly better way to set the initial trial vectors. But the improvement is really small
+and this flag at this moment is comparable with only LDA/PBE + NC PPs. So don't use it unless
+it's really necessary. 
+
+
+=====================================
+reference Default: 0 (Unit: Ry)
+
+One of the highlight variable. Use it to constrain the algorithm converge to these eigenstates
+having energy close to the reference. So one can calculate less eigenstates at once and do multiple
+calculations with different reference
+
+
+=====================================
+     broadening=0.005
+     start=0.0d0
+     finish=1.0d0
+     step=0.01d0
+
+Flags for ploting the spectrum. Meanings of them shoulbd be self-evident. All units are "Ry"
+
+=====================================
+     if_random_init=.false.
+
+Using preconditional random vectors as the trail vectors. Used only in special cases that you 
+do hate, and I don't see why, to calculate a few virtual states(Even the precision doesn't need
+to be high). Using bad trial vectors should cause only slow convergence, and don't affect the final 
+resulta.
+
+
+=====================================
+     p_nbnd_occ=10
+     p_nbnd_virt=10
+
+They are useful when there're too many occ/virt states pairs, and you care of only a few of them. 
+p_nbnd_occ and p_nbnd_virt indicate how many occ and virt states you would like to look at.
+In priciple they affect only the interpretation of the eigenstates, but no influence to their energy
+and the spectrum. 
+Make sure that min(p_nbnd_occ,nbnd_occ)*min(p_nbnd_virt,nbnd_virt) is lager than the number of initial
+vectors, so you won't end up using rendom trail vectors which will slow down your convergence. 
+
+
+=====================================
+     poor_of_ram=.false.
+
+When this set to true, you double the memory used for USPP calculation, but you get rid of applying many
+times of s_psi and cal_bec calculation, which takes a lot of time (sometimes more than half of the whole
+calculation) when the size of sub space is more than 100. 
+

TDDFPT/Examples/README

@@ -17,5 +17,6 @@ CH4-PR: Tests charge response algorithm
 SiH4: Tests Ultrasoft PP implementation
 CH4-BOND: This is an example that shows visual analysis of a softened bond in a set of degenerate bonds. 
 tools: Tools to compare data. 
+CH4-DAV: Example of using davidson algorithm