collation of responses on ab initio/first principles
Here as promised are responses to my question (see end of this posting) about the terms 'ab initio' and 'first principles'. Thanks to respondents.
I was not so much interested in the origin of the term ab initio but of course the answers are interesting. My real aim was to discover whether there is an intended subtle shift in meaning in using "first principles" rather than ab initio. None of the responses indicate that this might be so.
This idea arose from a recent conversation I had with Roald Hoffman who implied that this is the case.
Also, I was particularly interested in the posting from Per Ola Norrby who discusses how basis sets are constructed in a semi-empirical manner especially regarding expansion coefficients and contraction. I would be interested in learning more about this aspect and/or references to where it is discussed in the literature. 
 Further comments to me on any of these issues are welcome.
 eric scerri
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 Date: Mon, 26 Nov 2001 15:25:41 +0000 (GMT)
 From: Stuart Purdie <sdjp ^at^ st-andrews.ac.uk>
 X-Sender: sdjp ^at^ st-and.ac.uk
 To: Eric Scerri <scerri ^at^ chem.ucla.edu>
 Subject: Re: CCL:usage of terms "ab initio" and "first
 principles"
 Status: RO
 As I use the terms, they are interchangeable, meaning that the
 calculations are performed without recourse to any experimental measurent.
 This would include Hartree-Fock, and many of the DFT functionals, along
 with quantum monte carlo and CI methods.
 In actuallity, I belive they are taken to include all DFT, rather than
 spliting that particular hair.
 First principle seems to be used because the latin in ab initio can been
 seen as unnessecerily elitist.
 Stuart Purdie
 School of Chemistry
 University of St Andrews
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 Date: Sat, 24 Nov 2001 12:39:04 -0500
 From: elewars <elewars ^at^ trentu.ca>
 Subject: CCL:usage of terms "ab initio" and "first
 principles"
 To: chemistry ^at^ ccl.net
 X-Accept-Language: en
 Sender: "Computational Chemistry List" <chemistry-request ^at^
 ccl.net>
 Status: RO
 2001 nov 24
 Hello,
 Re the term _ab initio_", Dewar said:
 ""The term ab initio was originally applied to the Roothaan=Hall (RH)
 approach
 through an amusing accident. Parr was collaborating in some work of this kind
 with a group in England. In reporting one of his calculations, he described it
 as "ab initio", implying that the whole of that particular project had
 been
 carried out from the beginning in his laboratory. The term, unfortunately,
 became ..." See M. J. S. Dewar, "A Semiempirical Life", ACS,
 Washington, DC,
 1992; p. 129 (series Profiles, Pathways and Dreams, autobiographies of eminent
 chemists). Dewar was the leading champion of semiempirical methods over ab
 initio ones, and I do not know if Robert Parr ever commented on the above
 account.
   I don't know if "first principles" was introduced to play down the
 claim that
 ab initio is purely theoretical; certainly high-accuracy methods like G2 and G3
 are calibrated with experimental data, something which would have amused Dewar.
 E. Lewars
 ======
 ----------------------------------------
 Hi Eric,
This is not what you asked for, but I want to throw in a quick thought about those "empirical" parameters in DFT. It's not always realised that what is called "ab initio" incorporates many empirical parameters. For example, a standard HF/6-31G* calculation would be called "ab initio", but all the exponents and contraction coefficients in the basis set were selected by fitting to experimental data! That's one of the main reasons for the success of the Pople basis sets, they have been fit to real data, thus they are good at reproducing real data. The effect, of course, is that the basis set incorporates systematical errors that to a large extent cancels the systematical errors in HF ...
Thus, if you do a HF/6-31G* calculation on a standard organic molecule, you implicitly use 20-30 parameters that have been fit to experiment. If you instead use B3LYP, you add three more parameters. I don't think the difference between, for example, 30 and 33 parameters is sufficient to introduce a distinction in the degree of "empiricalness" of the methods.
Naturally, the above is not limited to the Pople sets. Any basis set with fixed exponent and/or contraction coefficients have at some point been adjusted to fit some data. I'm not completely sure, but I think that the main difference is that the Pople parameterization of basis sets used molecular data, whereas most others use atomic data. Thus, the Pople sets are good for molecules, whereas others of the same size are better for atoms.
I have yet not seen a true "ab initio" calculation for a molecule of a size that interests me... 
 	Best,
 	Per-Ola
 --
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Per-Ola Norrby, Assoc. Professor, http://compchem.dfh.dk/PeO/
 Technical University of Denmark, Dept. of Chem., Org. Chem.
 Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
 Email: pon ^at^ kemi.dtu.dk  tel +45-45252123,  fax +45-45933968
 -----------------
 Date: Sat, 24 Nov 2001 11:17:59 +0100
 From: Thomas.Heine ^at^ chiphy.unige.ch
 Subject: Re: CCL:usage of terms "ab initio" and "first
 principles"
 To: Eric Scerri <scerri ^at^ chem.ucla.edu>
 X-Comment: This message was scanned against viruses by lima.unige.ch.
 Status: RO
 Dear Eric,
 in my experience first principles was mainly used by physicists, already in
 times DFT was not in fashion in chemistry. Chemists used ab initio these days
 for everything HF-like and beyond.
 When chemists discovered DFT some of them started to use first principles to
 characterise their DFT calculations, especially those using CPMD. Perhaps to
 avoid confusion?
 I think it's similar for the use of SCF, which means in chemistry HF, and in
 physics simply the technique of solving the KS (or, if you want HF) equations.
 Have a nice weekend
 Thomas
 -------------------------------------------------
 X-Sender: sabrash ^at^ facstaff.richmond.edu
 Date: Sat, 24 Nov 2001 01:54:54 -0500
 To: Eric Scerri <scerri ^at^ chem.ucla.edu>
 From: "Samuel A. Abrash" <sabrash ^at^ richmond.edu>
 Subject: Re: CCL:usage of terms "ab initio" and "first
 principles"
 Status: RO
 Eric,
 	First principles has been used for a long time, as a vernacular
 alternative to ab initio.  The distinction you're talking about may be
 recent.  Freed, though, would say that DFT is semiempirical.
 Best,
 Sam Abrash
 At 10:17 PM 11/23/01 -0800, you wrote:
 
 I am interested in discovering the origins and current usage of the terms
 "ab initio" and "first principles" in computational work.
 Am I correct in thinking that the latter was introduced relatively
 recently, because one can no longer claim that practically
 implemented DFT methods are truly ab initio given the 'fixing' of
 density gradients by reference to experimental data.
 So although in terms of translation the two terms are virtually
 synonymous the usage implies that "first principles" is not quite so
 "ab initio"?
 I would appreciate comments and/or references to articles which may
 have discussed this question or first suggested such terminology
 regarding "first principles" as an alternative.  I will post
 responses.
  Eric Scerri ,
 
 --
 Dr. Eric Scerri ,
 UCLA,
 Department of Chemistry & Biochemistry,
 607 Charles E. Young Drive East,
 Los Angeles,  CA 90095-1569
 USA
 E-mail :   scerri ^at^ chem.ucla.edu
 tel:  310 206 7443
 fax:  310 206 2061
 Web Page:    http://www.chem.ucla.edu/dept/Faculty/scerri/index.html
 Editor  of  Foundations of Chemistry
 http://www.wkap.nl/prod/j/1386-4238
 Also see International Society for the Philosophy of Chemistry
 http://www.georgetown.edu/earleyj/ISPC.html