Optimal structure of cover letter for PhD application submitted directly to PI I am currently applying for PhD positions (mainly - though not exclusively - around Germany and Switzerland). As I would like to start as soon as possible and would rather be paid than receive a scholarship, I am not applying via grad schools but directly to potential supervisors.

This is an arduous process as very many PIs interest me, though most do not have the financial freedom of creating new PhD positions on the spot. Consequently I have written a lot of emails and I have developed a short formula which I adapt to each individual PI. The structure is roughly:


Title: 2-3 buzzwords related to the PIs work followed by " - PhD Opportunities"
Introductory statement - Who am I
Short summary of my experience, explicitly mentioning points relevant to his focus and including a link to my full CV
Explicitly state my preferred topics related to his focus
Explicitly ask if he has a PhD position opening, possibly including a suggestion of what sort of project would motivate me, and what about him/his group precisely I found interesting.


Here is an example e-mail:


  Neurogenetics and Psychopharmacology - PhD Opportunities
  
  Hello, I am a Molecular Neuroscience major from Heidelberg. I have
  recently graduated from our MSc. program and am currently looking for
  groups in which to pursue my PhD.
  
  I have very versatile experience in neuroscience - ranging from
  molecular biology, microscopy, and genetics in model animals up to
  fMRI, eye tracking, pupillometry, and behavioural tests in humans (for
  more on this please refer to my CV:
  http://chymera.eu/docs/cv-acad-gen.pdf ). I would like to continue
  using a broad spectrum of methods in my research, and put my scripting
  experience (Python, R, Julia, MATLAB, SPM, FSL) to good use in the
  analysis of complex data sets.
  
  I am very motivated by research into mood disorders and genetics; and
  I would also like to augment my methods spectrum with
  psychopharmacology and NIBS over the following years. I find the
  addition of these methods particularly important because in my opinion
  they present the most solid ways of testing causality in correlations
  between human brain activation and behaviour (as observed via fMRI or
  PET).
  
  I have browsed your list of publications and I found your
  neurogenetics work most motivating. I would like to ask you whether
  you would be able to offer me a PhD position in which I could
  integrate the genetic focus of your group with brain imaging and brain
  stimulation (perhaps to elucidate brain area function or
  psychopharmacological treatment possibilities resolved for
  endophenotypes). I would also be grateful for the opportunity to
  discuss further project ideas with you.
  
  Best Regards,
  
  Christian


I generally just write one email, and follow up 7-14 days later with a second one if there is no reply within the first week. Of the PIs that do not respond to the first email less than 25% respond to the second.

With this email structure (and what I believe is a strong background) I get a reply rate of ~50%, of which all replies specify that the PI would like to take me on - in principle. Actual invitations for interviews, however, are at about 5%. I am thinking this could be a lot better.

Do you have any (different) email structure which you have found optimal? Are there any other details - such as tone and style - which you think are very important to note in such a context?
I would say you are waiting too long to explain why you are interested in the research group. Your motivation for writing and taking up the faculty members' time should come much earlier in the message—I'd recommend no later than the second paragraph.

I'd also suggest that you might also want to consider sending the message to the Oberingenieur or Akademischer Rat of the faculty members' group; he or she may have a better idea of what vacancies are currently available.

Finally, "cold calling" does not get a high response rate; if there isn't an active opening, most potential advisors won't really respond unless they have to.